or bent fibrils in a tubular form and sealing the two adjacent edges by heating the tube at a suitable temperature this sheet may be formed of one layer of eptfe or of a multitude of layers of eptfe including two or more the layers may be heated for formation of a seal between said layers the inside of the tube is coated with a first material and the outside of the tube is coated with a second material where the same material is used for the inside and outside of the tube the coating may be accomplished by immersing the tube in a bath of the coating material or through other suitably coating techniques including spraying the coating painting the coating onto the tube or extruding the material onto the interior and exterior of the tube where different materials are used for the inner and outer layers the coating may be applied by spraying the tube painting the material on the tube extruding the materials or any other suitable application process immersion techniques may also be employed if the portion not being coated is appropriately masked the resulting tube may either be used directly as a balloon or more desirably as a balloon preform for additional processing so as to form a balloon therefrom in the latter case the preform may be shaped at a predetermined temperature through suitable balloon forming techniques as are known in the.