This specification covers a butyl (IIR) rubber in the form of sheet, strip, tubing, extrusions, and molded shapes.

This product has been used typically for parts such as grommets requiring resistance to phosphate esters or low permeability to gases, but usage is not limited to such applications. Not suitable for use in contact with petroleum-base fluids due to excessive swell. AMS3238 is no longer valid for O-rings and other compression seals. For O-rings and other compression seals, the requirements of AMS7338 shall be met wherever AMS3238 is specified.