Bulding on howste & Marc's replys...the only way to choose the proper material for a sealing application to know the specific sealing requirements...the sealing location & type of seal, tempratures (both high & low temp needs), pressures, any specific chemical resistance required, etc., etc. Kalrez® is an otstanding sealing material, but it is expensive. Has another material been tested? If yes, what was the failure mode. The only reason I suggested an off-line conversation is quite often, the specific of an application are confidential and someone may not wish to post them in an open forum.