bonding process has been found to be particularly advantageous when the polyurethane is applied to the flame treated silicone surface in the form of a liquid such as in a solvent or as a reactive liquid suitable solvents include organic solvents such as dimethyl acetamide dmac dimethyl formamide dmf and tetrahydrofuran thf any known flame treatment may be used to oxidise at least part of the surface of the silicone or silicone based material the range of suitable parameters for the flame treatment are as follows the oxygen ratio detectable after combustion from 0 05 to 5 preferably from 0 2 to 2 treatment speed from 0 1 m min to 2000 m min preferably from 10 m min to 100 m min treatment distance from 1 mm to 500 mm preferably from 2 mm to 50 mm many gases are suitable for flame treatment including natural gases pure combustible gases such as methane ethane propane and hydrogen or a mixture of different combustible gases the combustion mixture also includes air pure oxygen or oxygen containing gases the surface of the silicone is preferably treated with a blue flame at temperatures in the range of 1550 u00b0 c to 3000 u00b0 c and the resultant surface has an excellent adhesion with the polyurethane the flame treatment may be performed using any suitable known apparatus such as a burner based on natural gas such as propane butane or methane the flame treatment should be done.