Low density porous elastic cross-linked polymeric materials and their preparation

An elastic cross-linked porous polymer derived from vinyl polymerization of a mixture of monomer, comprising from about 2% to about 20% of a difunctional unsaturated cross-linking monomer, up to 50 weight % styrene and at least 50 weight % of a monomer selected from the group consisting of an alkyl acrylate, methacrylate and mixtures thereof, said polymer having a porosity in the range 75 to 95% internal phase volume and having interconnected pores, said pores having a mean pore diameter in the range 15 .mu.m to 80 .mu.m, said polymer having an elastic return from 50% compression to 90% of initial thickness of less than 120 seconds.