As far as I know, that's what all the breathable fabrics are. GoreTex ís PTFE (teflon™) with microscopic pores, originally developed for uranium refining; PTFE

As far as I know, that's what all the breathable fabrics are. GoreTex ís PTFE (teflon™) with microscopic pores, originally developed for uranium refining; PTFE is soft, so it's usually combined with a nylon shell. Tyvek comes in many varieties, one of which is a waterproof+breathable version; it's polyethylene fiber pressed into a porous felt-like sheet.