Sponge rubber, also referred to as cellular / foam / expanded rubber, is manufactured using a foaming agent that produces an air-filled matrix structure within the rubber. Sponge O-rings have less than 40A shore hardness. Rubber Seals & Gaskets manufactures sponge O-rings which not only offer excellent thermal stability across a wide range of temperatures, but also commendable properties of vibration, cushioning and damping. O-rings of sponge are available in a variety of materials such as silicone, EPDM, nitrile, etc.