Kalrez® & Chemraz® (Perfluoroelastomer)
(Kalrez is a perfluoroelastomer manufactured by DuPont Dow Elastomers; Chemraz is a perfluoroelastomer manufactured by Greene Tweed.) These elastomers combine the chemical resistance of Viton and fluoropolymers, making it far superior to most other elastomers. However, because of its high cost it is only used where absolutely required. It is only available inO-ring and sheet form so it cannot be used with all valve designs.