Silicone foams

A foamable silicone composition comprising a polysiloxane having silicon-bonded hydrogen atoms, a polysiloxane having siloxane units including unsaturated groups, a polysiloxane having silicon-bonded hydroxyl groups, a noble metal catalyst and from 3 to 40 parts by weight per 100 parts by weight of the composition of entities of borosilicate or silicate glass or mixtures thereof, the composition comprising first and second Parts having viscosities which are sufficiently similar to each other to permit facile machine mixing of the Parts and the first Part comprising the noble metal catalyst and a portion of the entities and the second Part comprising the polysiloxane having silicon-bonded hydrogen atoms and a portion of the entities pretreated with a compatible silane or polysiloxane having silicon-bonded hydrogen atoms, wherein said entities comprise hollow spherical particles and are selected from those having a bulk density (as determined by ASTM D 3101-72) between about 0.07 and about 0.25 g/cm.sup.3, a particle density (as determined by ASTM D 2840-69) of between about 0.1 and about 0.6 g/cm.sup.3, a particle size gradation of about 5 to about 250 microns, an average particle diameter from about 30 to about 80 microns, a wall thickness from about 1 to about 2 microns and a pressure resistance (as measured according to ASTM D 3102-72) from about 60 Bar to about 150 Bar.