# 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. - [A New Fluoropolymer for Stronger Wires and Molded Parts](https://patentbrief.org/patent/us/12735562/copolymer-injection-molded-body-member-to-be-compressed-and-covered-wire) — This patent describes a specific type of plastic, a copolymer made with tetrafluoroethylene and perfluoro(propyl vinyl ether), designed to be easily molded and used in things like electrical wires and compressed parts, thanks to its precise chemical makeup and properties. - [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.