Gore-Tex is a brand of expanded PTFE (ePTFE), a material incorporating a fluoropolymer membrane with micropores. The roof of the Hubert H. Humphrey Metrodome in Minneapolis , US, was one of the largest applications of PTFE coatings. 20 acres (81,000 m 2 ) of the material was used in the creation of the white double-layered PTFE-coated fiberglass dome.