A composition for forming a silicone elastomer, said composition comprising: A) a linear organopolysiloxane having at least two silicon-bonded ethylenically unsaturated groups per molecule; B) a linear organohydrogensiloxane having at least two silicon-bonded hydrogen atoms per molecule; at least one cross-linker C) selected from the group consisting of; C1) an organopolysiloxane having at least three silicon-bonded ethylenically unsaturated groups per molecule, and C2) an organopolysiloxane having at least three silicon-bonded hydrogen atoms per molecule; and D) a hydrosilylation catalyst present in a catalytically effective amount; wherein at least one of the silicon-bonded ethylenically unsaturated groups of component C1) has a lower reactivity relative to the silicon-bonded ethylenically unsaturated groups of component A); and wherein at least one of the silicon-bonded hydrogen atoms of component C2) has a lower reactivity relative to the silicon-bonded hydrogen atoms of component B); provided that if a molar excess of component B) is present relative to component A), then at least component C1) is present, and if a molar excess of component A) is present relative to component B), then at least component C2) is present. A) a linear organopolysiloxane having at least two silicon-bonded ethylenically unsaturated groups per molecule; B) a linear organohydrogensiloxane having at least two silicon-bonded hydrogen atoms per molecule; at least one cross-linker C) selected from the group consisting of; C1) an organopolysiloxane having at least three silicon-bonded ethylenically unsaturated groups per molecule, and C2) an organopolysiloxane having at least three silicon-bonded hydrogen atoms per molecule; and C1) an organopolysiloxane having at least three silicon-bonded ethylenically unsaturated groups per molecule, and C2) an organopolysiloxane having at least three silicon-bonded hydrogen atoms per molecule; and D) a hydrosilylation catalyst present in a catalytically effective amount; wherein at least one of the silicon-bonded ethylenically unsaturated groups of component C1) has a lower reactivity relative to the silicon-bonded ethylenically unsaturated groups of component A); and wherein at least one of the silicon-bonded hydrogen atoms of component C2) has a lower reactivity relative to the silicon-bonded hydrogen atoms of component B); provided that if a molar excess of component B) is present relative to component A), then at least component C1) is present, and if a molar excess of component A) is present relative to component B), then at least component C2) is present. wherein at least one of the silicon-bonded ethylenically unsaturated groups of component C1) has a lower reactivity relative to the silicon-bonded ethylenically unsaturated groups of component A); and wherein at least one of the silicon-bonded hydrogen atoms of component C2) has a lower reactivity relative to the silicon-bonded hydrogen atoms of component B); provided that if a molar excess of component B) is present relative to component A), then at least component C1) is present, and if a molar excess of component A) is present relative to component B), then at least component C2) is present.