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.

What it 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.

What it doesn't 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.

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.

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)