# 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. - **Patent:** US 3953566 - **Original title:** Process for producing porous products - **Owner:** WL Gore and Associates Inc - **Granted:** 1976 - **Status:** Public domain (expired) - **Times cited:** 1,364 - **Field:** materials, consumer_electronics, automotive, aerospace, medical, textiles, industrial_manufacturing ## What it does 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. ## 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. ## 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. ## Real-world examples 1. Gore-Tex waterproof-breathable fabrics 2. Surgical grafts and sutures 3. Industrial filters 4. Cable insulation 5. Dental floss (Glide floss) ## Why it matters 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. ## 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. **Full plain-English explainer:** https://patentbrief.org/patent/us/3953566/gore-tex-expanded-ptfe **Original patent:** https://patents.google.com/patent/US3953566 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [The Discovery of Teflon](https://patentbrief.org/patent/us/2230654/teflon-ptfe-polymer) — This 1941 patent describes the creation of polytetrafluoroethylene, a slippery, heat-resistant plastic discovered by accident that became known as Teflon. - [How Plastic Soda Bottles Are Made Stronger Using Stretched Molecules](https://patentbrief.org/patent/us/3733309/pet-plastic-bottle) — A 1970s invention that describes how to make lightweight, clear plastic bottles strong enough to hold carbonated drinks without exploding. - [How George de Mestral Invented Velcro](https://patentbrief.org/patent/us/2717437/velcro-hook-and-loop) — A 1952 patent describing the creation of a hook-and-loop fastener by weaving synthetic loops into fabric and cutting them to create tiny, grippy hooks. - [How Spandex Elastic Fibers Are Chemically Engineered](https://patentbrief.org/patent/us/2929804/spandex-lycra-elastic-fiber) — DuPont's 1960 patent for a stretchy, durable synthetic fiber made from segmented polymers, which became the foundation for modern Spandex. - [How Bubble Wrap Is Manufactured](https://patentbrief.org/patent/us/3142599/bubble-wrap-cushioning) — A 1959 manufacturing process that creates cushioning material by trapping air between two layers of plastic film.