Combination tube is made by overwrapping vulcanized fiber tube with epoxy resin saturated fiberglass filaments.  The angle of filament winding is usually set at 55°.  Vulcanized fiber tube becomes an integral tube liner which provides gas-generating and arc-quenching characteristics.  Epoxy resin saturated fiberglass provides strength and water resistance.  The combination tube is usually coated with UV resistant paint in gray color. 

Fiberglass/vulcanized fiber combination tube has the following advantages over fiberglass/polymeric synthetics combination tube: no-spark generating, char layer forming to prevent liner from excessive ablation, and the optimum amount of arc-quenching gas generating.  The main application of fiberglass/vulcanized fiber combination tube is used in expulsion fuse tube cutout for interrupting high voltage AC circuits during power surge.