ExFil 400 Strontium sulfate Excalibar Minerals Extenders / Fillers >> Strontium Sulfate/Celestite Rubber - Elastomer (Chloroprene, Butyl …) PU - Prepolymers ADHESIVE SEALANT CELESTITE PRODUCTS ~ STRONTIUM SULFATE Excalibar Minerals' Strontium Sulfate products are manufactured from a high quality ore, and processed to control the quality and consistency needed for use as fillers for rubber, plastic, urethane foams, paints & coatings, adhesives and caulks. Celestite. Possesses high quality and consistency. Used as filler for rubber, urethane foams, adhesives and caulks.