A key blade — the flat metal tongue that slides into a lock — has exactly one acceptable shape: the shape that fits the keyway and turns the pins. Change the profile and the key stops working. When the Federal Circuit confronted a design patent on the appearance of such a blade, it had no trouble striking it down. The blade had to look the way it looked, so there was nothing ornamental left to protect. Best Lock Corp. v. Ilco Unican Corp., 94 F.3d 1563 (Fed. Cir. 1996).

Now hold that case next to another. Ford holds design patents on the appearance of its F-150 truck hood. A hood, too, is profoundly functional: it must cover the engine, hinge open, shed water, and bolt to the body of that truck. Aftermarket parts makers argued the hood's appearance was therefore "functional" and the patents invalid. They lost. Automotive Body Parts Ass'n v. Ford Global Techs., LLC, 930 F.3d 1314 (Fed. Cir. 2019).

Two highly functional articles. Two opposite results. The difference between them is the whole subject of this article — and the reason "functionality" is the single most muddled doctrine in design patent law. Practitioners who are perfectly comfortable with trademark functionality, with the abstract-idea exclusion in utility patents, or with the idea-expression divide in copyright nonetheless stumble on a deceptively simple question: when does the fact that a product works a certain way defeat a patent on how it looks? Courts have answered inconsistently for more than a century, and the resulting case law is genuinely confused — not because judges are careless, but because the single word "functionality" has been quietly assigned two very different jobs. The confusion has drawn sustained scholarly attention; recent academic work, such as Professor Peter S. Menell and Ella Corren's "Design Patent Law's Identity Crisis" (UC Berkeley School of Law), has reignited debate over the proper role of functionality and, in the process, surfaced some of the persistent misconceptions this article sets out to dispel.

This article is written for three readers at once: the judge or law clerk who needs the doctrine laid out with pin cites; the patent or litigation attorney who needs a working framework for prosecution and trial; and the inventor, designer, or business owner who simply wants to know what a design patent can and cannot do. Every term of art is explained in plain language the first time it appears, and clearly labeled hypotheticals (using invented companies such as "Acme Corp.") illustrate the abstractions.

The thesis is simple. The muddle dissolves the moment you recognize that design-patent functionality is really two doctrines wearing one name. The first is a validity rule rooted in the statute: a design is unpatentable if its overall appearance is "dictated solely by function." That is the rule that killed the key blade. The second is a claim-scope rule that operates at infringement: how do individual functional features within a valid, ornamental design affect the breadth of what the patent actually covers against accused products? Keep those two questions separate and the case law snaps into focus. Blend them — as courts and litigants repeatedly have — and you get the muddle. Best Lock and Automotive Body Parts differ because the key blade flunked the first inquiry while Ford's hood, for all its utility, did not.

Two Doctrines, One Word: A Map Before the Territory

Before walking through the statute and the cases, it helps to hold the destination in view. When a lawyer says a design is "functional," she might mean either of two distinct things.

Functionality as an invalidity defense. Here the question is whether the entire claimed design, considered as a whole, is dictated solely by function. If so, the design fails the statutory requirement that it be "ornamental," and the patent is invalid. This is an all-or-nothing inquiry about the article as a whole. It rarely succeeds, because the bar — solely dictated by function — is deliberately demanding. The key blade is its natural home.

Functionality as a claim-construction and infringement consideration. Here the design is conceded (or found) to be valid and ornamental, but the patent contains some features that exist primarily for utilitarian reasons. The question becomes how those functional features bear on the scope of the claim — how much the patent actually protects when a court compares the patented design to an accused product through the eyes of an "ordinary observer."

These are not two flavors of the same test. They carry different legal consequences (death of the patent versus a narrower-or-broader scope), they use different units of analysis (the whole design versus particular features), and, as the Federal Circuit eventually had to clarify, they call for different methodologies. A great deal of doctrinal grief — and a number of reversals — traces to courts importing the rhetoric of one inquiry into the other. We return to this map repeatedly below.

A related boundary deserves emphasis at the outset: design-patent functionality is not the same as trade-dress functionality. Both doctrines police the line between protectable appearance and unprotectable utility, and they share intellectual DNA, but they are governed by different statutes, different tests, and different policy concerns. Trade-dress functionality — under the Lanham Act and TrafFix Devices, Inc. v. Marketing Displays, Inc., 532 U.S. 23 (2001) — asks, in part, whether a feature is "essential to the use or purpose" of the article or affects its cost or quality. Design-patent functionality asks whether the appearance is dictated solely by function. The two can reach opposite results on the same product. We explore that contrast in our companion piece on design patents versus trade dress protection for product configurations, and again in our survey of the evolution of trade dress protection for product design and configuration. Conflating the two is the single most common error we see in briefs, and this article assumes the reader wants to keep them straight.

The Statutory Foundation: 35 U.S.C. § 171 and the Ornamentality Requirement

Everything begins with the design patent statute. Section 171 provides:

"Whoever invents any new, original and ornamental design for an article of manufacture may obtain a patent therefor, subject to the conditions and requirements of this title."

The general provisions of the Patent Act apply to design patents "except as otherwise provided," 35 U.S.C. § 171(b), so the familiar requirements of novelty (§ 102), nonobviousness (§ 103), and adequate disclosure (§ 112) all carry over. But three statutory words do the distinctive work for our purposes, and each repays close reading.

"Ornamental." This is the operative word for functionality. A design patent protects ornamental appearance — the way an article looks — not the way it works. The Federal Circuit has repeatedly explained that to be ornamental a design must be "primarily ornamental rather than primarily functional," and must have been "created for the purpose of ornamentation rather than dictated purely by functional considerations." See PHG Techs., LLC v. St. John Cos., 469 F.3d 1361, 1366 (Fed. Cir. 2006); Ethicon Endo-Surgery, Inc. v. Covidien, Inc., 796 F.3d 1312, 1328 (Fed. Cir. 2015); In re Carletti, 328 F.2d 1020, 1022 (C.C.P.A. 1964); see also Blisscraft of Hollywood v. United Plastics Co., 189 F. Supp. 333, 337 (S.D.N.Y. 1960), aff'd, 294 F.2d 694 (2d Cir. 1961). Ornamentality is, importantly, a low bar in one sense — courts deliberately refuse to judge aesthetic merit or beauty — but a real bar in another: a design whose appearance is purely a byproduct of how the thing must work is not "ornamental" at all. The classic statement of how low the aesthetic threshold sits comes from the Second Circuit (in an era when Learned Hand sat on that court): an ornamental design need have only "at least a rudimentary aesthetic appeal." H. C. White Co. v. Morton E. Converse & Son Co., 20 F.2d 311 (2d Cir. 1927). The point is not that the design must be beautiful, but that it must reflect some visual distinctiveness — some non-trivial variation from a purely functional form — rather than being nothing more than the inevitable shape the article's mechanism forces upon it.

"Design for an article of manufacture." This phrase ties every design patent to a physical (and increasingly, a graphical) object that serves some utilitarian purpose. The Supreme Court has explained that an "article of manufacture" is broad — "simply a thing made by hand or machine," covering both a finished product sold to a consumer and a component of that product. Samsung Elecs. Co. v. Apple Inc., 137 S. Ct. 429, 434–35 (2016). But a design cannot float free of an article; an abstract picture standing alone is not patentable subject matter. See Ex parte Donaldson, No. 90-3471, 1992 WL 470726, at *2 (B.P.A.I. 1992). The USPTO now treats a computer-generated icon as satisfying the article-of-manufacture requirement so long as it is shown on a display. Because the underlying article always has some utility, the seeds of the functionality problem are planted in the statute itself: design patents live, by definition, on objects that do things.

"New" and "original." These words connect design patents to the novelty and nonobviousness requirements that govern all patents. We address obviousness — and the seismic change wrought by the en banc LKQ decision — in a dedicated section below and in our companion analysis of the LKQ decision and the shift in design patent obviousness.

The deep structural point is this: the statute itself creates a duality. A patentable design must simultaneously be ornamental (or it does not qualify) and attached to an article of manufacture (which is inherently utilitarian). The functionality doctrine is the law's attempt to manage that built-in tension — to grant exclusivity over appearance without granting, through the back door, exclusivity over the underlying utility that belongs, if anywhere, to a utility patent. For the bigger picture of what a design patent is and how it differs from its cousins, see our primer on patent basics.

Why the Duality Is a Feature, Not a Bug

It is tempting to treat the form-function overlap as a flaw to be policed out of the system. It is better understood as an accurate reflection of how product design works in the real world. Consider a chair. Its function is to support a seated person. Yet chairs come in essentially infinite ornamental variety — Shaker ladderbacks, Eames molded shells, Baroque thrones, stackable cafeteria seats. Each performs the identical function; each looks entirely different. It is precisely that layer of aesthetic variation, riding on top of a shared utilitarian purpose, that the design patent system exists to protect.

The Federal Circuit articulated this duality early and clearly. In Avia Group International, Inc. v. L.A. Gear California, Inc., 853 F.2d 1557 (Fed. Cir. 1988), the court drew the crucial distinction between the functionality of an article and the functionality of a particular design of that article:

"A distinction exists between the functionality of an article or features thereof and the functionality of the particular design of such article or features thereof that perform a function. Were that not true, it would not be possible to obtain a design patent on a utilitarian article of manufacture, or to obtain design and utility patents on the same article."

That sentence is the doctrinal keystone. The fact that an athletic shoe has a sole, laces, and an upper — all functional — does not mean a design patent on the particular appearance of that shoe is forbidden. Otherwise no useful object could ever be the subject of a design patent, which would gut § 171 entirely. The law instead asks a narrower question: is the specific ornamental treatment of those functional features dictated solely by function, or does it reflect choices that could have been made differently? In L.A. Gear itself, the answer was the latter — the shoe's design survived, because nothing about basketball required that arrangement of overlays, eyestay, and trim.

The corollary — that the same product can carry both a utility patent and a design patent without offending any "channeling" principle — is so important to practice that we devote a separate article to it: the intersection of design and utility patents. The short version is that dual protection is not a loophole; it is the system working as designed, because the two patents protect different things. The utility patent protects how the article works regardless of appearance; the design patent protects how the article looks regardless of how it works.

The Validity Question: "Dictated Solely by Function"

We turn now to the first of our two doctrines — functionality as an invalidity defense — and to the test that governs it.

From "Dictated by Function" to the Whole-Design Inquiry

The earliest cases asked, loosely, whether a design was "dictated by function." That phrasing proved unstable, because almost every design is influenced by function to some degree, and courts disagreed about how much influence was fatal. The modern formulation tightens the standard considerably: a design is invalid for functionality only where its overall appearance is "dictated solely by" the function of the article. The word "solely" is load-bearing. A design heavily shaped by functional considerations is still patentable so long as that appearance was not the only one that could perform the job.

Two features of the validity inquiry must be kept firmly in mind. First, it is judged for the claimed design as a whole, not feature by feature. The question is whether the overall appearance is dictated solely by function — not whether this or that individual element happens to serve a purpose. A design can be crowded with functional features and still be valid if their combined appearance reflects available choices. Second, the defense is rarely successful, precisely because most useful articles can be made to look many different ways while performing identically. The "solely dictated by function" standard screens out only the unusual case where form and function have genuinely collapsed into one another.

The Multi-Factor Test: Berry Sterling and PHG Technologies

The Federal Circuit has candidly acknowledged that it "has not provided a definitive test" for when a design is dictated by function. Instead, it has identified a set of factors that bear on the inquiry. The seminal articulation came in Berry Sterling Corp. v. Pescor Plastics, Inc., 122 F.3d 1452 (Fed. Cir. 1997), and the factors were applied and refined in PHG Technologies, LLC v. St. John Cos., 469 F.3d 1361 (Fed. Cir. 2006), and again in Automotive Body Parts Ass'n v. Ford Global Technologies, LLC, 930 F.3d 1314, 1319 (Fed. Cir. 2019). The non-exhaustive factors a court may weigh include whether:

  1. The protected design represents the best design for the article's function — a design that is the single optimal solution is more likely to be dictated by function.
  2. Alternative designs would adversely affect the utility of the article — if the only ways to change the appearance would also impair how the thing works, that cuts toward functionality.
  3. There are any concomitant utility patents covering the article or its features — a utility patent on the same elements is evidence that those elements were chosen for what they do, not how they look.
  4. The advertising touts particular features of the design as having specific utility — if the patentee's own marketing sells the shape as a functional advantage, that is telling.
  5. There are any elements in the design, or an overall appearance, clearly not dictated by the function of the article — even one ornamental flourish unrelated to function helps establish ornamentality.

These are weighed together; none is dispositive standing alone. The Federal Circuit has been explicit on two related points that practitioners should commit to memory. First, the presence of alternative designs that achieve the same function, "although not dispositive, increases the likelihood that a design is primarily ornamental." Second — and this trips up litigants who import trademark thinking — the mere fact that a design has aesthetic appeal to consumers does not render it functional. Automotive Body Parts, 930 F.3d at 1319. Consumer attraction to a look is the point of an ornamental design, not evidence against it.

The Alternative-Designs Inquiry, Properly Understood

The availability of alternative designs is the most useful evidentiary tool in the functionality analysis, but it is widely misdescribed. It is not a freestanding "test" that mechanically decides validity. It is a powerful factor that usually proves dispositive in practice for a simple reason: there are almost always other ways to make a useful article look different while still working.

The classic illustration is Bergstrom v. Sears, Roebuck & Co., 496 F. Supp. 476 (D. Minn. 1980), involving a tubular fireplace grate that circulated heated air by convection. The court acknowledged that function might dictate the general "C" shape of such a grate, but reasoned that function did not dictate the particular configuration the patentee chose, because a "myriad of alternatives" existed in the appearance of convective grates. The existence of those alternatives compelled the conclusion that the patent was not invalid for functionality. The logic is the L.A. Gear logic applied to a homely object: function may constrain the broad category, but ornamental choice survives within it.

Worked example (hypothetical). Suppose Acme Corp. obtains a design patent on the appearance of a hand-held barcode scanner. The accused infringer, Beacon LLC, argues the design is invalid because a scanner must have a grip, a trigger, and a scanning window. Under the proper inquiry, those facts are nearly irrelevant. The question is whether the overall appearance Acme claimed — the particular silhouette, the angle of the grip, the proportions of the housing, the placement and shaping of the trigger guard, the surface contours — was the only appearance a working scanner could have. Beacon would have to show that competing scanners cannot be designed to look meaningfully different without losing utility. Because the market is full of scanners that all work but look distinct, Acme's design almost certainly survives. Beacon's better arguments lie not in validity but in scope — the second doctrine, to which we will return.

When Functionality Actually Wins: The Best Lock Lesson

Validity challenges based on functionality do succeed, occasionally, and the paradigm case is the one that opened this article: Best Lock Corp. v. Ilco Unican Corp., 94 F.3d 1563 (Fed. Cir. 1996). The patent claimed the ornamental design of a key blade. The court found the design invalid because the blade had to have that exact profile to fit and operate the corresponding keyway. There was no alternative blade shape that would work in the same lock; the appearance and the function had genuinely merged.

Best Lock is the exception that proves the rule. It marks the narrow band in which the "solely dictated by function" standard bites — where the design's appearance is so completely constrained by an external mating requirement that no aesthetic latitude remains. The instinct it captures, that an interface dictated by a counterpart leaves no room for ornament, also explains the European Union's separate "must-fit" exclusion, discussed below. But for the overwhelming majority of articles, where designers enjoy real freedom of expression within functional constraints, the design survives the validity challenge.

The Scope Question: Functionality in Claim Construction and Infringement

We now cross from the first doctrine to the second — and this is where most of the historical confusion lives.

How a Design Patent Is Infringed: The Ordinary Observer Test

To see why functionality matters at infringement, recall how design-patent infringement is judged. Since the Supreme Court's decision in Gorham Co. v. White, 81 U.S. (14 Wall.) 511 (1871), and as reaffirmed and streamlined by the en banc Federal Circuit in Egyptian Goddess, Inc. v. Swisa, Inc., 543 F.3d 665 (Fed. Cir. 2008), infringement turns on the ordinary observer test: whether, in the eye of an ordinary observer giving such attention as a purchaser usually gives, the accused design is substantially the same as the patented design — so similar that the observer would be deceived into buying one supposing it to be the other. After Egyptian Goddess, the comparison is conducted in light of the prior art, but it remains a holistic, side-by-side comparison of overall visual impressions, not an element-by-element checklist. See also Ethicon, 796 F.3d at 1335; Int'l Seaway Trading Corp. v. Walgreens Corp., 589 F.3d 1233, 1239–40 (Fed. Cir. 2009). A recent wrinkle: the comparison prior art a defendant offers to narrow the field must itself be applied to the same article of manufacture as the claimed design. Columbia Sportswear N. Am., Inc. v. Seirus Innovative Accessories, Inc., 80 F.4th 1363, 1378 (Fed. Cir. 2023).

Because the patent protects only ornamental appearance, functional features matter to this comparison. If two products look alike only because they share functional features that any competing product would necessarily have, that shared appearance should not, by itself, prove infringement. The hard question — the one that produced years of inconsistent decisions — is how a court should account for functional features when construing the claim and applying the ordinary observer test. (For a deeper treatment of how claim construction shapes design cases, see our overview of design patents in patent litigation.)

The "Factoring Out" Era: Richardson v. Stanley Works

For a period, the Federal Circuit's answer seemed to be that courts should factor out (or "filter") the functional aspects of a design before comparing it to the accused product. The high-water mark was Richardson v. Stanley Works, Inc., 597 F.3d 1288 (Fed. Cir. 2010). The patent covered a multi-function carpentry tool combining a hammer, crowbar, jaw, and handle. The Federal Circuit affirmed a non-infringement judgment and approved language stating that the district court "properly factored out the functional aspects of Richardson's design as part of its claim construction." Id. at 1293–94. The court reasoned that because a design patent protects only ornamental features, the "purely functional" aspects of the design should be removed from the scope of the claim before comparison.

Read literally and aggressively, Richardson invited a methodology with serious problems. It risked rewriting the claimed design: the USPTO examined and allowed a design defined by drawings showing the whole article, and surgically deleting elements at litigation changes the very thing the public was told had been patented. It undermined public notice: a core function of any patent is to tell the world, clearly, what is protected, and if scope can shrink unpredictably when functional elements are excised in court, competitors cannot reliably design around the patent. (For more on the notice function of patents in litigation, see our guide to patent infringement litigation from summary judgment to post-trial.) And it was unworkable: deciding which elements are "functional" enough to delete is subjective, and removing an element from a unified visual design distorts the very overall impression the ordinary observer test exists to evaluate.

These problems set the stage for a course correction.

The Course Correction: Ethicon Endo-Surgery v. Covidien

The leading modern decision is Ethicon Endo-Surgery, Inc. v. Covidien, Inc., 796 F.3d 1312 (Fed. Cir. 2015), involving design patents on ultrasonic surgical shears — the trigger, the activation buttons, and the torque knob of a handheld surgical instrument. The Federal Circuit used Ethicon to clarify what Richardson did and did not mean.

The crucial holding is that a functional feature is not automatically excised from a design; rather, functional features can themselves carry protectable ornamental aspects. As the court put it, functional features "may also have protectable ornamental design elements." Id. at 1332. The fact that a trigger must pull, or a knob must turn, does not strip the particular shape and appearance of that trigger or knob of all protection. The correct approach is not to delete functional elements but to construe the claim to identify the ornamental aspects of the design as shown in the drawings, including the ornamental aspects of features that also serve a function.

Ethicon also reaffirmed the right unit of analysis for infringement: the comparison is of the overall appearance of the claimed design as it appears on the accused product, "as opposed to isolated features." Id. at 1335; see also OddzOn Prods., Inc. v. Just Toys, Inc., 122 F.3d 1396, 1405 (Fed. Cir. 1997) ("There can be no infringement based on the similarity of specific features if the overall appearance of the designs are dissimilar."). In other words, courts must neither ignore functionality nor let it become a license to dismantle the claimed design into pieces.

Sport Dimension v. Coleman: No Element May Be Eliminated

If Ethicon corrected the interpretation of Richardson, Sport Dimension, Inc. v. Coleman Co., 820 F.3d 1316 (Fed. Cir. 2016), supplied the rule's sharpest edge. The patent covered the ornamental design of a personal flotation device — a life vest — and the district court, reading Richardson aggressively, had construed the claim to eliminate the armbands and side torso tapering altogether because they served the functional purpose of flotation. The Federal Circuit reversed.

The court announced the governing principle with unusual clarity: in none of its prior cases had it "entirely eliminate[d] a structural element from the claimed ornamental design, even though that element also served a functional purpose." Id. at 1320–22. A court may not remove a structural element from a claimed design simply because the element is functional. Even where features are functional, the design as a whole — the way those features are shaped, proportioned, and arranged — remains the protected subject matter and must be considered in the infringement comparison. The proper response to functional features is to recognize that they may limit the scope of the claim (because the patentee cannot claim the function), not to delete them from the design.

Sport Dimension carries a practical wrinkle the Federal Circuit itself flagged: when the appeals court modifies a claim construction in this area, the infringement question often becomes "unclear" under the new construction, frequently requiring remand. Id. at 1323. That uncertainty is the price of getting the analysis right, and it is one more reason to nail down the functionality posture early in a case.

Where the Scope Doctrine Stands Today

Synthesizing Richardson, Ethicon, and Sport Dimension, the contemporary rule can be stated in a few sentences. A design patent protects only ornamental features, so a court construing the claim must account for the reality that some features exist for functional reasons and cannot be monopolized as functions. See OddzOn, 122 F.3d at 1405; Richardson, 597 F.3d at 1293. But the court does not delete functional elements; it recognizes that functional features can carry ornamental aspects (Ethicon), and it never eliminates a structural element from the claimed design entirely (Sport Dimension). The ultimate infringement question remains the holistic Gorham/Egyptian Goddess comparison of overall ornamental appearance, conducted in light of the prior art.

The net effect on scope is intuitive once the doctrine is untangled. Functionality does not invalidate the typical design patent, but it does narrow it. Where a design is crowded with features that any competitor must include to make a working product, the ornamental "signal" carried by those shared features is weak, and the patent will tend to be infringed only by products that are very close visual copies. Where a design contains distinctive ornamental flourishes untethered to function, the patent is correspondingly stronger and reaches a wider range of accused products. Functionality, in short, is less a kill switch than a dimmer.

Worked example, continued (hypothetical). Return to Acme's barcode scanner. Beacon's scanner also has a grip, a trigger, and a window — but those shared functional features prove little, because every scanner has them. The infringement question is whether the overall ornamental appearance of Beacon's scanner — its particular proportions, contours, and surface treatment — is substantially the same as Acme's in the eyes of an ordinary purchaser, viewed against the backdrop of other scanners in the prior art. If Acme's claimed design has distinctive curves and a signature housing profile and Beacon copied them, Acme likely wins despite the shared functional skeleton. If the two scanners resemble each other only in the unavoidable functional respects, Beacon likely prevails. Crucially, no court will delete the grip or trigger from Acme's claim; it will simply recognize that those features, being common to all scanners, contribute little to the protected ornamental impression.

When Functionality Reaches the Money: The Article-of-Manufacture Problem

There is a third place functionality does quiet but consequential work, and most treatments skip it: the damages stage. Section 289 of the Patent Act gives a design-patent owner a remarkable remedy — the infringer's total profit on the "article of manufacture to which [the patented design] has been applied," with a statutory floor of $250, on top of (or as an alternative to) the ordinary reasonable-royalty and lost-profits damages available under § 284. 35 U.S.C. §§ 284, 289; see Catalina Lighting, Inc. v. Lamps Plus, Inc., 295 F.3d 1277, 1291 (Fed. Cir. 2002).

The phrase "total profit" once seemed to mean total — disgorge every dollar earned on the entire end product, even if the patented design adorned only one part of it. That reading produced the headline judgments in the smartphone wars, where Apple recovered Samsung's entire profit on infringing phones. The Supreme Court reversed in Samsung Elecs. Co. v. Apple Inc., 137 S. Ct. 429 (2016), holding that the relevant "article of manufacture" can be either the end product or a component of it, depending on the facts. Id. at 434–36. Where a patented design covers only a component, the recoverable profit may be limited to the profit on that component.

Here is the functionality connection, and it is one litigants routinely miss. Identifying the right "article of manufacture" for damages is, in part, an exercise in figuring out where the protected ornamental design begins and ends — which features actually embody the claimed appearance versus the surrounding functional structure that the design does not, and cannot, monopolize. The same instinct that narrows claim scope at infringement (functional features carry little ornamental weight) tends to narrow the article-of-manufacture base at damages (the disgorgeable article is the thing that bears the ornamental design, not necessarily the whole machine). A defendant who concedes infringement of a design on a phone's faceplate has every incentive to argue that the "article" is the glass-and-bezel front, not the entire phone — and the more functional the surrounding components, the stronger that argument. Functionality, having quietly shaped validity and scope, shows up one last time to size the check.

Automotive Body Parts v. Ford: Aesthetic Functionality and the Right to Repair

No discussion of design-patent functionality is complete without the second case that opened this article: Automotive Body Parts Ass'n v. Ford Global Technologies, LLC, 930 F.3d 1314 (Fed. Cir. 2019). The case arose from Ford's design patents on the appearance of an F-150 truck hood and headlamp. An association of aftermarket parts makers, who wanted to sell replacement hoods and headlamps that necessarily looked like Ford's so they would fit and match the truck, attacked the patents on two theories the Federal Circuit squarely rejected.

The "aesthetic functionality" theory. The aftermarket sellers argued that because consumers want a replacement part that matches the original vehicle's appearance, the matching appearance is itself "functional" — borrowing the aesthetic-functionality concept from trademark law, where a feature can be functional if exclusive use would put competitors at a significant non-reputational disadvantage. The Federal Circuit refused to import that doctrine into design patent law. It held that the aesthetic appeal of a design — including a consumer's desire for a part that matches — does not render the design functional for § 171 purposes. Id. at 1319–20. The very purpose of a design patent is to protect an ornamental appearance that consumers find attractive; the fact that they are attracted to it cannot be the thing that destroys it. This holding draws the bright line between trademark functionality and design-patent functionality that we flagged at the outset, and it is why the two doctrines must never be casually merged. (For the trademark side of that line, see the evolution of trade dress protection for product design and configuration.)

The "no alternatives in the repair market" theory. The aftermarket sellers also argued that, because the only way to make a matching replacement part is to copy Ford's design, no real alternatives exist and the design is therefore functional. The court rejected this too, clarifying how the alternative-designs factor actually works. The relevant question is whether alternatives exist for the original article's appearance at the time of design — Ford could have styled the hood and headlamp many ways — not whether a competitor in the repair market has alternatives to copying once Ford's design is on the road. The desire to copy for compatibility is not a functional constraint on the design; it is simply a desire to free-ride on a protected ornamental design. Id. at 1319–21.

The repair and exhaustion arguments. The association further argued that patent exhaustion and an implied "right to repair" should let purchasers obtain replacement parts that embody the patented design. The Federal Circuit disagreed, holding that exhaustion applies to the particular articles Ford sold, not to the design embodied in new replacement parts the aftermarket makers wished to manufacture, and that the right to repair does not extend to reconstructing or reproducing the patented design in entirely new components. Id. at 1321–24.

Automotive Body Parts therefore matters far beyond automotive parts. It confirms three propositions: (1) consumer attraction to a look, even attraction driven by a desire to match, is not "functionality"; (2) the alternative-designs inquiry is anchored at the moment of original design, not at the moment a copyist wants to compete; and (3) design patents can lawfully constrain the aftermarket. That last point places the decision at the center of an active policy debate, which we examine in our coverage of the right to repair movement and its IP implications. Legislatures in several jurisdictions have considered "repair clause" exceptions that would limit design-patent enforcement against replacement parts, and the European Union has long had such a clause for visible spare parts. Whether the United States follows is a live question; as a matter of current doctrine, Automotive Body Parts is controlling.

Functionality at the USPTO: Examination and Prosecution Strategy

Functionality is not solely a litigation concern. Unlike copyright registration — which involves no substantive examination of the merits — a design patent application is examined by the USPTO. An examiner assesses novelty under § 102, nonobviousness under § 103, and, critically for us, ornamentality under § 171. The Manual of Patent Examining Procedure addresses functionality directly, instructing examiners that a design must be ornamental and not "the result of, or merely an incidental byproduct of, functional or mechanical considerations." See MPEP § 1504.01(c). The MPEP also reminds examiners that a design must be "preconceived" and not merely "a chance result of a particular method or combination of functional elements." See MPEP § 1504.01.

Examiners weigh the same kinds of considerations that govern litigation: whether alternative designs exist that perform the same function, whether the applicant's own advertising touts the utility of the claimed features, whether a related utility patent covers the same article, and whether design features are visible during normal use (features hidden in use are less likely to be ornamental). When an examiner concludes a design is primarily functional, the application draws a § 171 rejection for lack of ornamentality.

For applicants facing such a rejection — or, better, seeking to avoid one — several drafting and prosecution strategies are effective:

  • Marshal evidence of alternative designs. Demonstrating that the same function can be achieved by visibly different designs is the most direct route to overcoming a functionality rejection. Catalogs, competitor products, and the applicant's own design iterations all serve.
  • Use broken (dashed) lines deliberately. In design patent drawings, solid lines define the claimed design and broken lines show unclaimed environment or context. By rendering purely functional or unimportant structure in broken lines, an applicant can focus the claim on the ornamental features and disclaim the elements most vulnerable to a functionality attack. This is among the most powerful and underused tools in design prosecution. (For the mechanics of capturing a design before filing, see how to prepare an invention disclosure for your patent attorney.)
  • Be careful what the marketing says. Because the "advertising touts utility" factor cuts against ornamentality, applicants and their marketing teams should avoid promotional copy that sells a claimed shape as a functional advantage. A press release boasting that "our uniquely contoured grip reduces fatigue" can later be quoted against the very design patent on that grip.
  • Consider multiple embodiments and a thoughtful title. Filing several visual variations can help show that the design reflects ornamental choice rather than functional inevitability, and a carefully drafted title accurately identifies the article without unduly narrowing scope.
  • Pair the design with a utility filing where appropriate. If the genuine innovation is functional, the right home for it is a utility patent, with the design patent reserved for the genuinely ornamental appearance. Coordinating the two — and managing the double-patenting issues that can arise — is the subject of our companion piece on the intersection of design and utility patents. Applicants navigating examiner rejections generally will also benefit from our broader guide to responding to patent office actions.

Functionality After LKQ: Obviousness and the Validity Picture

In 2024, the en banc Federal Circuit transformed design-patent obviousness law in LKQ Corp. v. GM Global Technology Operations LLC, overruling the long-standing Rosen/Durling framework and replacing it with the more flexible Graham v. John Deere obviousness analysis familiar from utility patents. We analyze that decision in depth in the LKQ decision and the seismic shift in design patent obviousness, and the headline is that design patents are now somewhat easier to challenge as obvious, because challengers are no longer constrained by the rigid requirement of a single primary reference "basically the same" as the claimed design.

LKQ did not change the functionality doctrine. Obviousness (§ 103) and functionality/ornamentality (§ 171) are distinct validity inquiries: obviousness asks whether the design would have been obvious to a designer of ordinary skill in light of the prior art, while functionality asks whether the design is dictated solely by function. But the two interact in practical litigation, and LKQ matters to the functionality story in two ways.

First, by lowering the obviousness barrier, LKQ gives accused infringers a stronger alternative validity theory. A defendant who once might have strained to fit a weak functionality argument now has a more potent obviousness attack available. We expect functionality to be pleaded somewhat less often as the lead invalidity theory and more often as a scope-narrowing argument at infringement, where (as we have seen) it does its most reliable work. For the obviousness doctrine generally, our guide to overcoming obviousness rejections under § 103 supplies the utility-patent backdrop LKQ now imports into the design world.

Second, LKQ's embrace of the Graham framework reinforces a theme that runs through the modern functionality cases: the design must be analyzed for its overall ornamental appearance, judged from the perspective of the relevant skilled or ordinary observer, against the backdrop of real-world alternatives. The same evidentiary record — competitor designs, the range of available appearances, the relationship of features to function — that informs the functionality inquiry also informs the post-LKQ obviousness inquiry. Sophisticated litigants will build that record once and deploy it for both purposes.

The bottom line after LKQ: functionality remains a narrow validity defense that rarely kills a design patent outright, but it is now one tool in a broader and more flexible invalidity toolkit, and its most dependable role is in shaping claim scope at infringement.

A Note on International Approaches

Functionality is a global concern, and companies seeking worldwide design protection should know that the standards vary, even though most converge on a similar core idea.

The European Union, under its design regulation, excludes features of appearance that are "solely dictated by [the product's] technical function." The Court of Justice's decision in DOCERAM GmbH v. CeramTec GmbH, Case C-395/16 (CJEU 2018), clarified that the test is whether technical function was the only factor that determined the features, assessed objectively in light of all relevant circumstances — not merely whether alternative forms exist. The EU also has a separate "must-fit" exclusion (covering interface features that must take a precise form to connect to another product — the analog to Best Lock's key blade) and, importantly for the repair debate, a "must-match" repair clause for visible spare parts, a notable contrast with the U.S. result in Automotive Body Parts.

Japan excludes designs "indispensable for securing the function" of the article, but Japanese courts read the exclusion narrowly, generally allowing protection unless the form is the only way to achieve the function — a posture close to the U.S. "solely dictated" standard.

China has historically taken a comparatively strict line against designs dictated mainly by technical function, though recent reforms (including the introduction of partial design protection and a longer term aligned with the Hague system) have added flexibility for designs that blend ornamental and functional features.

For U.S.-based filers, the practical lessons are to expect roughly harmonized but not identical functionality standards, to consider the Hague System for streamlined multi-jurisdiction filing, and to plan separately for the EU and other repair-clause regimes where aftermarket enforcement may be limited even when the underlying design is valid.

Putting It All Together: A Step-by-Step Framework

For a practitioner confronting a design-patent functionality issue — whether in prosecution, an opinion letter, or litigation — the following sequence keeps the two doctrines separate and the analysis disciplined.

  1. Identify which question you are actually answering. Is the issue validity ("is this patent dead for functionality?") or scope ("how much does this valid patent cover?")? Almost every error starts with skipping this step.
  2. For validity, apply the whole-design "solely dictated by function" standard. Use the Berry Sterling/PHG/Automotive Body Parts factors: best design, effect of alternatives on utility, concomitant utility patents, advertising touting utility, and any elements clearly not dictated by function. Remember that consumer appeal is not functionality, and that the defense rarely succeeds outside Best Lock-type situations where appearance and mechanism have merged.
  3. For scope, do not delete functional features. Following Ethicon and Sport Dimension, recognize that functional features may carry ornamental aspects and that no structural element is eliminated from the claimed design. Construe the claim around the ornamental appearance shown in the drawings.
  4. Apply the ordinary observer test to overall appearance. Under Gorham and Egyptian Goddess, compare the patented design's overall ornamental impression to the accused product, in light of the prior art, asking whether an ordinary purchaser would be deceived. Shared functional features carry little weight; distinctive ornamental ones carry much. Confirm that any comparison prior art is drawn from the same article of manufacture (Columbia Sportswear v. Seirus).
  5. Map functionality onto the damages base. If infringement is found, identify the right "article of manufacture" for § 289 total-profit recovery under Samsung v. Apple — the thing that bears the ornamental design, which may be a component rather than the whole product.
  6. Build the alternative-designs record once. Evidence of the range of available appearances supports the validity defense, informs scope, and now also feeds the post-LKQ obviousness analysis. Anchor the alternatives inquiry at the time of original design, not at the moment a copyist wants in.
  7. Coordinate with adjacent protections. Decide whether utility patent, trade dress, or copyright (for separable artistic features under Star Athletica, L.L.C. v. Varsity Brands, Inc., 580 U.S. 405 (2017)) belongs alongside the design patent, and confirm that each protects its proper sphere without functionality problems of its own.

Key Takeaways

  • Functionality is two doctrines, not one. Validity (is the design dictated solely by function, judged as a whole?) and scope (how do functional features affect claim breadth at infringement?) are distinct. Most of the "muddle" comes from conflating them.
  • The validity defense is narrow. Under § 171 and the Berry Sterling/PHG/Automotive Body Parts factors, a design is invalid only if its overall appearance is dictated solely by function — a standard that, outside Best Lock-type cases, rarely defeats a patent.
  • Courts no longer "factor out" functional elements. Ethicon and Sport Dimension corrected the aggressive reading of Richardson: functional features can carry ornamental aspects, and no structural element is deleted from the claimed design.
  • Aesthetic appeal is not functionality. Automotive Body Parts holds that consumer attraction to a design — even a desire for matching replacement parts — does not make it functional, and refuses to import trademark "aesthetic functionality" into § 171.
  • Functionality reaches the damages base too. Under § 289 and Samsung v. Apple, the recoverable "total profit" turns on identifying the article of manufacture that bears the ornamental design — sometimes a component, not the whole product.
  • Design-patent functionality is not trade-dress functionality. The statutes, tests, and outcomes differ; keep them separate.
  • After LKQ, functionality is one tool among several. Obviousness is now a more flexible invalidity route, and functionality does its most dependable work narrowing claim scope at infringement.

Frequently Asked Questions

Does the presence of functional features invalidate a design patent? No. Virtually every article protected by a design patent has functional features — that is what it means to be an "article of manufacture." A design is invalid only if its overall appearance is dictated solely by function. The existence of functional features, without more, proves nothing.

Can a single product have both a utility patent and a design patent? Yes, and it is common. The utility patent protects how the article works; the design patent protects how it looks. Because they protect different things, there is no improper "double dipping." Coordinating the two does raise double-patenting and timing issues, addressed in our companion article on the intersection of design and utility patents.

What is the difference between design-patent functionality and trademark/trade-dress functionality? They are separate doctrines under separate statutes. Trade-dress functionality (under the Lanham Act and TrafFix) can defeat protection where a feature is essential to use or purpose or affects cost or quality, and it includes an "aesthetic functionality" branch. Design-patent functionality (under § 171) asks only whether the appearance is dictated solely by function, and the Federal Circuit has refused to import aesthetic functionality into it. See our comparison of design patents and trade dress for product configurations.

Do courts still "factor out" functional elements when comparing designs? No, not in the sense of deleting them. After Ethicon and Sport Dimension, courts recognize that functional features can carry protectable ornamental aspects and must not be eliminated from the claimed design. Functionality narrows scope; it does not erase features.

How does the alternative-designs inquiry actually work? The availability of other designs that achieve the same function strongly suggests a design is ornamental, not functional. After Automotive Body Parts, the inquiry is anchored at the time of the original design — could the article have been styled differently? — not at the moment a competitor wants to copy for compatibility.

How does functionality affect the money damages I can recover? It helps define the "article of manufacture" on which the infringer's total profit is measured under 35 U.S.C. § 289. After Samsung v. Apple, that article may be a component bearing the design rather than the entire end product, so the more the surrounding structure is functional and separable, the smaller the disgorgeable base may be.

Did the LKQ decision change the functionality doctrine? No. LKQ changed obviousness analysis for design patents, not the functionality/ornamentality test. But by making obviousness a more flexible invalidity route, it affects litigation strategy: functionality is increasingly used to narrow scope at infringement rather than as a lead invalidity theory.

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This article is provided by mclaw.io for general informational purposes only and does not constitute legal advice. Design patent functionality is a fact-intensive area in which outcomes turn on specific drawings, prosecution histories, and accused products. Reading this article does not create an attorney-client relationship. For advice regarding a particular design, application, or dispute, consult qualified patent counsel.