A multi part hydrosilylation curable silicone elastomer composition comprising (i) an organopolysiloxane comprising at least two unsaturated groups and having a viscosity of at least 1,000 mPas at 25.degree. C.; (ii) inorganic filler having a hydrophilic surface; (iii) a filler treating agent comprising an organopolysiloxane comprising at least 2 hydroxy or otherwise hydrolysable groups, or a mixture thereof and having an average degree of polymerisation of from 2 to 50; (iv) an organohydrogensiloxane having an average of greater than two silicon bonded hydrogen atoms per molecule having a viscosity of up to about 10 PaS at 25.degree. C.; (v) a hydrosilylation catalyst; and/or a treated filler obtained by the reaction of (ii) and (iii) above characterised in that the filler treating agent (iii) and/or treated filler is packaged separately from organohydrogensiloxane (iv) prior to curing.