Making Strong, Porous PTFE: The Gore-Tex Process
This patent describes a specific process for rapidly stretching a highly crystalline form of PTFE plastic to create a strong, porous material with a unique internal structure, forming the basis for products like Gore-Tex.
Original patent title: “Process for producing porous products”
This patent describes a specific process for rapidly stretching a highly crystalline form of PTFE plastic to create a strong, porous material with a unique internal structure, forming the basis for products like Gore-Tex. Granted to WL Gore and Associates Inc in 1976 with 25 claims and 1,364 forward citations, and it is now in the public domain.
Key facts
Coverage
What does this patent actually cover?
The patent describes a process (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 1) for making a porous product from a polymer of tetrafluoroethylene, also known as PTFE. First, a shaped article of "highly crystalline poly(tetrafluoroethylene)" is created using a "paste-forming extrusion technique." After removing any lubricant, this unsintered article is stretched at a very fast rate, "exceeding about 10% per second" (Claim 1), while kept at a temperature between about 35°C and the material's crystalline melt point (Claim 1). This rapid stretching creates a material with a unique microstructure of "nodes interconnected by fibrils," as mentioned in the abstractabstractA short summary at the front of the patent describing the invention. Not legally binding.Read more →, resulting in high porosity (Claim 13, 40-97%) and strength. For example, a PTFE rod could be stretched rapidly to become a porous tube, which could then be used in a waterproof fabric.
The gap
What does this patent NOT cover?
- Does not cover making porous PTFE by methods other than rapid stretching of a paste-extruded, highly crystalline PTFE article.
- Does not cover stretching PTFE at rates slower than about 10% per second (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 1).
- Does not cover stretching PTFE outside the temperature range of about 35°C and its crystalline melt point (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 1).
- Does not cover porous PTFE products made from materials that are not "highly crystalline poly(tetrafluoroethylene)" (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 1).
- Does not cover the final porous product itself, only the specific process of making it.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
What made this novel
The clever bit was discovering that rapidly stretching highly crystalline PTFE, specifically after paste extrusion and before sintering, creates a strong, porous material with a unique node-fibril structure. Previous methods often resulted in weak, torn, or non-porous material, but this specific combination of high stretch rate and controlled temperature yielded a robust, usable porous form.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Gore-Tex waterproof-breathable fabrics
Surgical grafts and sutures
Industrial filters
Cable insulation
Dental floss (Glide floss)
Why it matters
The bigger picture
This patent is foundational to the development of expanded PTFE (ePTFE), famously known by the brand name Gore-Tex. The process described enabled the creation of materials that are both waterproof and breathable, revolutionizing outdoor apparel, medical implants, and industrial filtration. It allowed WL Gore and Associates to build a multi-billion dollar business based on this unique material.
Filed
July 3, 1973
Granted
April 27, 1976
Market context
Who's building on this
Companies in this space
WL Gore and Associates Inc. continues to be the primary innovator and manufacturer of ePTFE products, building extensively on this foundational patent. Other companies also produce expanded PTFE, often under licenselicensePermission from the patent owner to make, use, or sell the invention — usually in exchange for payment. Doesn't transfer ownership.Read more → or using alternative processes that avoid the specific claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more → of this patent, for applications in medical devices, filtration, and sealing.
Market impact
This patent created an entirely new category of high-performance materials: expanded PTFE (ePTFE). It enabled the development of products like waterproof-breathable fabrics, revolutionizing outdoor gear and protective clothing. It also had a profound impact on the medical device industry, providing biocompatible materials for implants and grafts, and significantly advanced filtration and sealing technologies across various industrial sectors.
Claim 1 — Plain English
What this patent covers
The patent describes a process (Claim 1) for making a porous product from a polymer of tetrafluoroethylene, also known as PTFE. First, a shaped article of "highly crystalline poly(tetrafluoroethylene)" is created using a "paste-forming extrusion technique." After removing any lubricant, this unsintered article is stretched at a very fast rate, "exceeding about 10% per second" (Claim 1), while kept at a temperature between about 35°C and the material's crystalline melt point (Claim 1). This rapid stretching creates a material with a unique microstructure of "nodes interconnected by fibrils," as mentioned in the abstract, resulting in high porosity (Claim 13, 40-97%) and strength. For example, a PTFE rod could be stretched rapidly to become a porous tube, which could then be used in a waterproof fabric.
The clever bit
The clever bit was discovering that rapidly stretching highly crystalline PTFE, specifically after paste extrusion and before sintering, creates a strong, porous material with a unique node-fibril structure. Previous methods often resulted in weak, torn, or non-porous material, but this specific combination of high stretch rate and controlled temperature yielded a robust, usable porous form.
What it does not cover
- Does not cover making porous PTFE by methods other than rapid stretching of a paste-extruded, highly crystalline PTFE article.
- Does not cover stretching PTFE at rates slower than about 10% per second (Claim 1).
- Does not cover stretching PTFE outside the temperature range of about 35°C and its crystalline melt point (Claim 1).
- Does not cover porous PTFE products made from materials that are not "highly crystalline poly(tetrafluoroethylene)" (Claim 1).
- Does not cover the final porous product itself, only the specific process of making it.
Patent Journey
From filing to expiry
PatentBrief Score
Impact Score
Moderate
Citation count
40/40
Highly cited
Claim breadth
17/20
Very broad protection
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$94K – $300K
Midpoint $187K · expired or expiring · industry ×1.6
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
The original legal language
Original claims
25 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Gore, R. W. (1976). Making Strong, Porous PTFE: The Gore-Tex Process (U.S. Patent No. 3,953,566). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/3953566/gore-tex-expanded-ptfe
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does Making Strong, Porous PTFE: The Gore-Tex Process cover?
This patent describes a specific process for rapidly stretching a highly crystalline form of PTFE plastic to create a strong, porous material with a unique internal structure, forming the basis for products like Gore-Tex.
Who owns patent US 3953566?
WL Gore and Associates Inc owns this patent, granted in 1976.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 3953566 cited by?
This patent has been cited by 1364 later patents that build on its ideas.
What problem does this patent solve?
This patent is foundational to the development of expanded PTFE (ePTFE), famously known by the brand name Gore-Tex. The process described enabled the creation of materials that are both waterproof and breathable, revolutionizing outdoor apparel, medical implants, and industrial filtration. It allowed WL Gore and Associates to build a multi-billion dollar business based on this unique material.
What does this patent NOT cover?
Does not cover making porous PTFE by methods other than rapid stretching of a paste-extruded, highly crystalline PTFE article.
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