Rubber that is twice as light as cork is used in a new lifesaving jacket adopted by the U. S. Navy. Sponge rubber, which it resembles, is formed of cells that are largely intercommunicating; but the cellular rubber of the life jacket is made of cells walled off from each other, each cell containing a tiny bubble of gas. Ten times as resistant to water as cork or balsa, it could never absorb enough water to cause it to sink. Experiments are being made with this cellular rubber in pontoon bridges and life rafts. It is already being used in selfsealing gasoline tanks for airplanes, and as a heat insulator under the decks of “mosquito” torpedo boats.