A "Heat Exchanger Gasket" is a term that has been given to the gasket that is called out for use in an exchanger. The make up of the gasket or type varies due to the operating conditions of the exchanger. Some of the commonly used gaskets are metallic and soft compressible material.
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Construction of Metal Jacketed Gaskets

Metallic gaskets can come in different styles like; double jacket, single jacket, solid metal or a spiral wound. Soft compressible material can be rubber, PTFE, or non-asbestos compressed sheet type. The design of an exchanger also may require different gasket shapes and the ones mentioned above can be made to a variety of shapes.

Lamons jacketed gaskets are normally shipped with a non-asbestos high temperature filler. The standard filler is normally sufficient for applications up to 900º F. Other soft fillers are available for higher temperatures or special applications including Grafoil . Standard metals used to make jacketed gaskets, regardless of the type, are aluminum, copper, the various brasses, soft steel, nickel, Monel , Inconel and stainless steel types 304, 316, 321, 347, 410, 502. Obviously the choice of the metal used for the jacketed part of the gasket would depend upon the corrosive conditions being encountered.