Gore-Tex is a polytetrafluoroethylene (ePTFE) membrane (better known as a Teflon membrane) laminated on the inside of the garment to the outer shell (such as a nylon). Its intended function is to be wind and waterproof (rain gear) and yet be breathable. For our purposes we do not feel Gore-Tex breathes fast enough in the winter weather. We see moisture build-up on the inside of Gore-Tex garments most often on our winter camping trips. The warm body moisture moves outward and has to make it through the Gore-Tex membrane in order to get through to the outer shell. But, at this point the moisture has slowed down because it has hit a very cold outer wall. The body moisture begins to crystallize between the Gore-Tex membrane and lining and literally becomes ice if left outside (for example on a winter camping trip). Therefore, we use Supplex nylon which does not have a membrane laminate and is more breathable in colder conditions.