what id Gore-Tex
 

Gore-Tex is a material incorporating fluoropolymer membrane with micropores. The roof of the Hubert H. Humphrey Metrodome in Minneapolis is one of the largest applications of Teflon PTFE coatings on Earth, using 20 acres (81,000 m2) of the material in a double-layered, white dome, made with PTFE-coated fiberglass, that gives the stadium its distinctive appearance. The Millennium Dome in London is also substantially made of PTFE for PTFE lined ball valve