The filler material is completely enclosed by a two piece metal jacket, which covers both the inside and outside diameters and both contact surfaces Double Jacketed Gaskets are used on boiler and heat exchanger applications when ample bolting is available to correctly seat the gasket. They are designed for high pressure and temperature applications up to and inclusive of class 900. The temperature limitation of the gasket is dictated by the combination of metallic and non-metallic materials used in its construction.