The method of this invention admixes in a high shear mixer 100 parts by weight of polydiorganosiloxane gum plasticizer chopped organic or inorganic fibers, and then when the fibers are uniformly mixed from 1 to 60 parts of reinforcing silica filler. The uniform mixture is then heated with mixing, under vacuum, optionally with nitrogen containing catalyst, to treat the filler and remove any volatiles, then cooled to give a uniform mixture with the fibers well dispersed throughout the mixture.