Abstract: The present invention provides a heat-curable silicone rubber composition to be cured by hydrosilation reactions and having outstanding physical properties, especially a high tear strength, said composition comprising(A) a polydiorganosiloxane having at least two unsaturated aliphatic hydrocarbon groups and represented by the general formula (1):R.sub.a.sup.1 SiO.sub.(4-a)/2 ( 1)wherein R.sup.1 represents a substituted or unsubstituted monovalent hydrocarbon group containing 0.01 to 15 mole % of an unsaturated aliphatic hydrocarbon group, a is a positive number of from 1.95 to 2.05.(B) a polyorganohydrogensiloxane having at least three hydrogen atoms directly bonded to silicon atom in a molecule,(C) silica filler having a specific surface area of at least 50 m.sup.2 /g, and(D) an addition reaction catalyst,(E) water, and preferably(F) an organosilane represented by the general formula:R.sub.m.sup.2 Si(OR).sub.4-mwherein R.sup.

Abstract: The present invention provides a heat-curable fluorosilicone rubber composition to be cured by hydrosilation reactions and having outstanding physical properties, especially improved transparency and processability, said composition comprising(A) a polydiorganosiloxane having at least two unsaturated aliphatic hydrocarbon groups and represented by the general formula (1):R.sub.a.sup.1 SiO.sub.(4-a)/2 ( 1)wherein R.sup.1 represents a substituted or unsubstituted monovalent hydrocarbon group containing 0.01 to 15 mole % of an unsaturated aliphatic hydrocarbon group, a is a positive number of from 1.95 to 2.05.(B) a polyorganohydrogensiloxane having at least three hydrogen atoms directly bonded to silicon atoms in a molecule and represented by the general formula: ##STR1## wherein R.sup.2, R.sup.3 and R.sup.4 independently represents a substituted or unsubstituted monovalent hydrocarbon group, X represents CF.sub.2 or C.sub.3 F.sub.