Quite the opposite, sponge rubber often starts with expandable rubber styles like EPDM or neoprene. The rubber compound is then supplemented using a chemical blowing agent, which, on heating, decomposes and releases gases. This method results in the growth on the rubber as well as formation of the sponge-like structure. https://huameirubberfoam41952.acidblog.net/64917037/the-greatest-guide-to-water-proof-rubber-foam