Brand of waterproof/breathable fabric. GoreTex is a membrane attached underneath the outer fabric and protected on the inside by a nylon or mesh liner. Its pores are 700 times smaller than a water drop, but still large enough for perspiration vapor to pass through. Thus after several hours of wear you don't become damp from your own perspiration. It's also windproof. Not a necessity, but this and other brands with similar function perform well.

Not just the stuff of ski clothing: used in a special surgical specification as a barrier to the formation of peritoneal adhesions.