Varglas Non-Fray Sleeving is flexible, high-temperature secondary insulation made from closely braided, continuous filament fiberglass which has been heat-cleaned to remove impurities in the yarn and to retard fraying. There are four types available all of which are noncorrosive and nonflammable and not attacked by fungus. - Type HP - heat cleaned and treated with an acrylic resin binder (natural or pigmented) that is slightly more flexible than Type HO.