A photopolymerisable system is disclosed which can be polymerised by exposure to UV light, for example, to form a solid, light-transmitting sheet material having volume refractive index variations defining an optical diffuser or a hologram, for example. The system includes a silicone monomer, prepolymer, macromonomer or co-monomer capable of undergoing free radical initiated polymerization and further includes a photoinitiator.