Broadening Design Patent Scope Through Broken Lines in a Continuation: The Legal Boundaries and Practical Risks

Abstract: In the U.S. design patent system, broken lines are used not only to define the scope of protection but also as a tool for establishing priority and avoiding functionality defenses. As a form of "partial claiming," broken lines allow an applicant to seek protection for particular ornamental features of an article while treating the rest as unclaimed environment or boundary. But while that strategy can yield broader protection, it carries complex risks under the written description requirement, the prohibition on new matter, and prosecution history estoppel.

I. The Distinctive Context of U.S. Design Patents

Unlike utility patents, design patents protect the ornamental appearance of an article of manufacture. Under 35 U.S.C. § 171, a patent may be granted for "any new, original and ornamental design for an article of manufacture."

In early practice, the USPTO tended toward a strict reading, requiring the claim to cover the entire article. Commercial practice, however, showed that a product's distinctive visual appearance matters greatly to its competitiveness, and that design is an important asset in intellectual property competition. Product innovation is often concentrated in a particular portion of an article — the tread pattern of a sole, the bezel of an electronic device — and those features are frequently carried across a range of models. If the law required an applicant to depict and claim the entire product, a competitor could evade infringement by modifying non-core portions slightly.

Yet applicants face substantial uncertainty early on: they must file promptly to establish priority, while anticipating the design-arounds competitors may adopt once the product reaches market. Broken lines emerged to meet that need.

As a legal matter, solid lines define the claimed design while broken lines depict unclaimed environment or boundary. An applicant may file a design with detailed line work to secure priority and then, in a continuation, convert solid lines in the parent to broken lines — "broadening" the claim by "disclaiming" certain features. That strategy of subtraction in exchange for breadth has generated new disputes and risks in practice.

II. The Gatekeeper of Priority: Adequate Written Description in the Parent

For a continuation to claim the parent's filing date, it must satisfy 35 U.S.C. § 120 — which raises the question: where an applicant changes claim scope through broken lines in the continuation, did the parent provide adequate written description support?

In In re Salmon, 705 F.2d 1579 (Fed. Cir. 1983), the applicant sought to use the parent's filing date to avoid prior art.

Parent disclosure: a drawing of a stool with a square seat.

Continuation/CIP claim: a drawing of a stool with a round seat.

The dispute: the applicant argued that the parent disclosed the general concept of a "stool," that square and round were conventional variants of a stool seat, and that the parent should therefore support the round variant.

Holding: the Federal Circuit affirmed the rejection, establishing a strict "identity of invention" standard for design patents. In a design, the court explained, the drawing is the description. A square seat in the parent does not describe the appearance of a round seat. Unlike utility practice, design patents do not support deriving a genus (a seat of any shape) from a single embodiment (square) unless the parent expressly discloses that possibility.

The conclusion: for a continuation to claim the original filing date under § 120, the invention in the continuation must be adequately supported under § 112 by the original disclosure.

If the continuation is found to introduce new matter — a shape or boundary concept not disclosed in the original — it loses priority, and the original application (if published or granted) becomes prior art against it. Under 35 U.S.C. § 102, that leads directly to rejection or invalidity for lack of novelty — the phenomenon known as self-collision.

III. The Line in the Sand: The "Possession" Standard

In In re Owens, 710 F.3d 1362 (Fed. Cir. 2013), an employee of Procter & Gamble filed a design application for a mouthwash bottle.

Original application: a complete bottle, drawn entirely in solid lines.

Continuation: Owens sought to protect only a small portion of the bottle's shoulder and top. To define that scope, he introduced a broken boundary line across the pentagonal front panel, dividing it into upper and lower portions. The upper trapezoidal region remained in solid lines; the lower portion and the rest of the bottle were converted to broken lines.

The USPTO rejected the application, reasoning that the dividing line did not exist in the original application and that the resulting scope therefore constituted new matter. Owens invoked Daniels, arguing that the trapezoidal region was physically present and "clearly visible" within the original pentagonal panel and that the division should be permitted.

The Federal Circuit affirmed, establishing a stricter rule:

Visibility does not equal possession. That a region is visible in the original drawing does not mean the inventor regarded it as a distinct inventive subject at the filing date. The written description requirement demands not merely that a design be disclosed but that the inventor regarded that portion as his invention. In Owens, the parent disclosed only a complete pentagonal panel; nothing indicated the inventor had then conceived of a standalone "upper trapezoid."

No artificial boundaries. The line Owens drew fell across what was, on the original bottle, part of a smooth surface with no physical marking — no ridge, no color division, no change in material. A broken boundary line introduced in a continuation must have an explicit basis in the original application. Where the original design already contains a structural line, converting it to a broken boundary is permissible; drawing a line out of nothing to cut a continuous surface is not.

In Ex parte Bologna, Appeal 2018-006240 (PTAB 2019), the Board took an especially strict position. The applicant sought to protect a sports helmet design through a continuation. The original application showed the complete helmet. In the continuation, most solid lines were converted to broken lines, leaving only an irregularly shaped region on the side of the helmet in solid lines. Unlike Owens, the applicant drew no new broken boundary — the solid lines simply stopped and met the broken lines directly.

The Board affirmed the rejection, reasoning that although no explicit boundary was drawn, the edge of the solid-line region — where solid stopped and broken began — constituted in substance an invisible boundary. Because that location on the original application was a continuous curved surface with no physical feature defining the path of that invisible boundary, the amendment likewise violated the written description requirement.

Conclusion: an applicant may convert solid lines in the original drawing to broken lines, but may not cut the original solid-line region with a broken line that did not previously exist — unless that dividing line connects existing structural points and follows reasonably from the disclosure. Nor may an applicant draw an unclosed broken line that leaves the boundary between solid and broken indeterminate. An applicant cannot, in a continuation, stake out territory to cover a competitor's particular product unless that boundary is traceable in the parent.

IV. The Limits of Prosecution History Estoppel

In Advantek Marketing, Inc. v. Shanghai Walk-Long Tools Co., 898 F.3d 1210 (Fed. Cir. 2018), Advantek filed a design application for a pet gazebo.

Figures 1–4: the kennel without a cover. Figure 5: the kennel with a cover.

The USPTO issued a restriction requirement, treating these as two inventions and requiring an election. Advantek elected Figures 1–4 (the uncovered frame) and cancelled Figure 5, ultimately obtaining a patent on the uncovered kennel.

In subsequent infringement litigation, Walk-Long sold a kennel with a cover. Relying on Pacific Coast Marine, the district court ruled against Advantek on the ground that it had surrendered the covered embodiment during prosecution to obtain the patent and, under prosecution history estoppel, could not now assert infringement against a covered product.

The Federal Circuit reversed, adopting a reading favorable to the patentee.

The court explained that the uncovered kennel Advantek elected was in fact the broader design. A covered kennel necessarily contains the frame within it. Advantek's election of the frame was therefore not a narrowing to exclude covered kennels but an assertion of a broad right covering both the bare frame and the frame when covered.

"Advantek elected to patent the ornamental design for a kennel with a particular skeletal structure. A competitor who sells a kennel embodying Advantek's patented structural design infringes the patent, regardless of extra features, such as a cover, that the competitor might add to its kennel."

Prosecution history estoppel, the court clarified, exists to prevent an applicant from recapturing scope expressly surrendered to satisfy patentability requirements. Advantek had not surrendered the frame design within a covered kennel; by electing the frame embodiment, it had strengthened its claim to that structural feature. Walk-Long's product, though covered, copied the core frame structure and therefore fell within the claim.

Conclusion: under Advantek, using broken lines to extract a product's "skeleton" does not produce estoppel as to the complete product. It yields a strong patent covering every "skeleton plus accessory" combination — so that a competitor cannot design around by simply adding a cover, wheels, or a handle.

V. Conclusion

In U.S. design patent practice, converting solid lines to broken lines in a continuation is a powerful but high-risk strategy. Its legality turns on the written description requirement of 35 U.S.C. § 112 — on whether the inventor possessed the broader design in the original application.

An applicant may not, in a continuation, introduce an artificial boundary line undisclosed in the parent in order to carve out a new scope, nor create an invisible boundary through conversion alone. The better practice is therefore not to subtract blindly in a continuation, but to lay out layered defensive drawings at the original filing stage, and in continuation strategy to balance breadth of protection against the stability of the patent, so that enforceability is not compromised.

This article is provided for legal research and general reference only and does not constitute legal advice on any specific matter.