of silicon tetrachloride or ethyl silicate by precipitation means etc commercially available fumed silicas include cab o sil u00ae cabot corp and aerosil u00ae degussa inc fumed silica is preferred the treating agents used in the practice of this invention are fluoroalkyl functional polysiloxane fluids having a viscosity of from about 50 250 centipoise which may be formed from cyclic polysiloxane monomers that have been hydrolyzed to form a mixture of cyclics and short diorganopolysiloxane chains the cyclic polysiloxane entities will have from 3 9 siloxy units some of the larger ring structures arising from reformation of cyclic monomer starting materials the linear entities will have varying block lengths with the average degree of polymerization being about 5 they are typically fluid polymers having a low molecular weight usually under 1000 the cyclic polysiloxane starting materials are well known in the silicone elastomer art and are composed of from 3 to 8 siloxy units having the formula rch 2 ch 2 si me o where r is a perfluoroalkyl radical of from 1 to 10 carbons such as cf 3 c 2 f 5 c 7 f 15 and c 10 f 21 they may be prepared by methods disclosed in u s pat no 2 979 519 pierce et al and u s pat no 3 179 619 brown which are incorporated herein by reference the preferred starting compound is 3 3 3 trifluoropropylmethylsiloxane.