1.1 This specification covers white reinforced non-vulcanized polymeric sheet made from polyisobutylene (PIB) intended for use as a single-ply roof membrane exposed to the weather. The sheet shall be reinforced with fiber or fabric.1.1.1 The pol This specification covers fiber or fabric reinforced nonvulcanized white polymeric sheet made from polyisobutylene (PIB) intended for use as a single-ply roof membrane exposed to the weather. In-place roof systems design criteria such as fire resistanc