Thermosetting compositions which can be used to form molded articles and coatings comprising (1) organopolysiloxanes having at least 40 mol percent monoorganosiloxane units and at least 0.1 percent by weight of condensable groups, (2) fillers and/or reinforcing agents, (3) a condensation catalyst, if desired, and (4) diorganopolysiloxanes having a viscosity of at least 30 cSt at 25.degree. C. in which the diorganopolysiloxanes (4) are present in an amount of from about 15 to 30 percent by weight based on the organopolysiloxanes (1), and the mixture of organopolysiloxanes (1) and (4) forms two phases.