Home - Monmouth Rubber & Plastics Monmouth Rubber & Plastics has been a U.S. Manufacturer of Durafoam™ closed cell sponge rubber and plastic foam materials for more than 54 years. Monmouth Rubber & Plastics has been a U.S. Manufacturer of Durafoam™ closed cell sponge rubber and plastic foam materials for more than 54 years.