Federal Circuit Affirms USPTO’s Rejection of Multilayer Porous Film Patent in *In re: Kwangjin Song*

In a closed appellate decision finalized on February 18, 2026, the United States Court of Appeals for the Federal Circuit delivered a decisive affirmation of the USPTO’s rejection of a patent application covering an oriented multilayer porous film technology. In *In re: Kwangjin Song* (Case No. 25-1653), the Federal Circuit upheld the Patent Trial and Appeal Board’s (PTAB) invalidity determination, finding the appellant’s arguments unpersuasive across the board.

The case, which progressed through a 307-day appellate lifecycle, centers on U.S. Patent Application No. 15/707,151 (published as US20180043656A1). For patent prosecutors, IP portfolio managers, and R&D teams operating in the advanced materials and polymer film space, this ruling reinforces critical lessons about patentability standards at the USPTO and the appellate standards governing PTAB review at the Federal Circuit.

This outcome matters because oriented multilayer porous films have wide applications in battery separators, filtration membranes, and packaging—making patentability disputes in this space commercially significant.

Case Overview

The Parties

The Patent at Issue

This case centered on U.S. Patent Application No. 15/707,151, published as US20180043656A1, which relates to oriented multilayer porous film technology—engineered polymer films with controlled porosity and layered architecture used in high-performance industrial and consumer applications.

• • US Patent Application No. 15/707,151
• • Publication Number: US20180043656A1
• • Technology Area: Oriented multilayer porous film
• • Verdict Cause: Patentability — Invalidity/Cancellation Action

Litigation Timeline & Procedural History

The appeal was filed in the District of Columbia jurisdiction on **April 17, 2025**, following an adverse PTAB ruling on the patentability of Song’s multilayer porous film application. The case proceeded through the Court of Appeals for the Federal Circuit—the exclusive appellate venue for USPTO patent prosecution appeals under 35 U.S.C. § 141.

The 307-day duration from filing to closure reflects a relatively standard Federal Circuit appellate timeline for *ex parte* prosecution appeals, which typically move faster than inter partes contested proceedings. No chief judge assignment data was disclosed in the case record. The case resolved without disclosed oral argument details, suggesting the panel may have decided the matter on the briefs—a common outcome when appellant arguments are deemed legally insufficient to disturb PTAB’s factual findings.

The Verdict & Legal Analysis

Outcome

The Federal Circuit **affirmed** the PTAB’s decision in its entirety. The court’s dispositive language was unambiguous:

“We have considered appellant’s other arguments and find them unpersuasive. We affirm the Board’s decision. AFFIRMED.”

No damages were at issue, as this is a patent prosecution appeal rather than an infringement action. No injunctive relief was implicated. The practical effect of affirmance is that U.S. Application No. 15/707,151 remains rejected, and Song cannot obtain the patent claims as prosecuted through this appellate avenue.

Verdict Cause Analysis

The case falls under the **Patentability — Invalidity/Cancellation Action** classification, meaning the USPTO rejected Song’s claims on substantive patentability grounds during prosecution. While the full opinion’s specific legal reasoning (e.g., whether rejection was based on anticipation under 35 U.S.C. § 102, obviousness under § 103, or written description/enablement under § 112) is not detailed in the provided case data, the Federal Circuit’s wholesale dismissal of the appellant’s arguments as “unpersuasive” indicates the PTAB’s rejection was well-supported by the evidentiary record.

In multilayer porous film prosecution appeals, PTAB rejections frequently turn on:

• • Obviousness (§ 103): Prior art combinations demonstrating that layered porous film configurations were known in the polymer membrane art
• • Claim indefiniteness or enablement (§ 112): Insufficient specification support for claimed functional or structural parameters
• • Anticipation (§ 102): Specific prior art references disclosing oriented multilayer porous structures

The Federal Circuit applies a **deferential standard of review** to PTAB’s factual findings, reversing only when findings lack substantial evidence. The court’s terse affirmance strongly suggests Song failed to identify reversible legal error or unsupported factual determinations.

Legal Significance

This case reinforces several established Federal Circuit doctrines relevant to patent prosecution appeals:

1. Deference to PTAB factual findings: Absent clear legal error, the Federal Circuit will sustain Board rejections supported by substantial evidence—a high bar for appellants.
2. Burden on appellant: The appellant bears the burden of demonstrating that PTAB committed reversible error; broad disagreement with the Board’s conclusions is insufficient.
3. Technical prosecution record matters: The strength of the examiner’s and Board’s rejection, particularly in technically complex fields like polymer film architecture, is difficult to overcome without compelling counter-evidence or expert support.

Strategic Takeaways

For Patent Prosecutors and Applicants:

• Build a robust specification with detailed enablement support for structural and functional claim limitations in multilayer film applications
• Engage technical experts early during PTAB appeal briefing—the USPTO’s use of a Ph.D. attorney signals the technical credibility stakes
• Consider continuation strategy or claim amendment before exhausting appeals; affirmance at the Federal Circuit forecloses further prosecution on affirmed rejections

For IP Professionals:

• Monitor the published application (US20180043656A1) for freedom-to-operate relevance; a rejected application provides prosecution history insight into the claim scope the applicant sought but could not obtain
• Track related family members or divisional applications that may pursue narrower or differently drafted claims

For R&D Teams:

• The rejection of Song’s oriented multilayer porous film claims may signal room in the prior art landscape for competitors—but conduct formal FTO analysis before commercializing similar film architectures
• Document design decisions and engineering departures from prior art structures to support future patentability arguments

Industry & Competitive Implications

Oriented multilayer porous films represent a commercially vital technology class, with applications spanning **lithium-ion battery separators**, **medical filtration membranes**, **food packaging barriers**, and **industrial filtration systems**. The global battery separator market alone is projected to grow substantially through 2030, making IP protection in this space strategically valuable.

The Federal Circuit’s affirmance of USPTO’s rejection leaves the specific claim scope Song pursued unprotected, potentially widening the freedom-to-operate corridor for competitors developing similar multilayer porous film architectures. However, this outcome also signals that the prior art landscape in oriented porous film technology is sufficiently dense that broad or imprecisely drafted claims face significant patentability headwinds.

For companies holding existing patents in battery separator or polymer membrane technologies—including major players in the materials science sector—this ruling underscores the importance of **differentiated claim drafting** and **strong technical disclosure** to survive both USPTO examination and potential PTAB challenge. Licensing negotiations in this space should account for the evidentiary record that prosecution histories like Song’s create.