show fairly good abrasion but their viscosity is too high to be mixed or extruded in a thermoset silicone and shear heating would result in premature cure also as mentioned above the cost is much more than the silicone rubber compositions in accordance with the invention as either the fluoropolymer additive or the very large amount of u201c tough rubber u201d silicone base polymer used to increase the abrasion resistance adds excessive cost it is considered that certain amounts of toughened silicone rubber base polymer may be used in accordance with the invention however this is in contrast to comparative examples i and j wherein it is used in large quantities with only a microcrystalline silica additive comparative examples i and j had fairly good abrasion resistance but their cost is many times the formulations of the invention and their die c tear strength is below 100 examples 1 7 in accordance with the invention show the greatly improved abrasion resistance of the invention example 2 shows very high abrasion resistance at the lowest cost surprisingly precipitated silica additive sipernat 120 has a lower surface area and should presumably be less reinforcing but has better abrasion resistance than precipitated silica additive sipernat 160 examples with.