Hexamethylcyclotrisiloxane was polymerized at 60.degree. C by .gamma. radiation to yield filler free silicone rubber (FFSR). The G (crosslinking) value of 23.5 was found for the FFSR polymerized for 4 h, compared to about 2 for the pure polydimethylsiloxane (PDMS). The sol fractions for both FFSR and cross-linked PDMS varied between 5-7%. The FFSR and the cross-linked PDMS both had tensile strength of about 1 kg/cm2 but FFSR was not brittle and could be extended as much as 500% before breaking. The marked improvement in physical properties of FFSR may be due to the formation of domains of highly cross-linked material which act as internal filler.