Imagine a wet suit that goes on loose, then snugs down to keep you warm as you descend to icy depths. Thanks to smart-materials developer Mid Technology of Medford, MA, such suits are on the way. To make the suits work, Mid spikes neoprene, the standard wet suit material, with isopropylacrylamide, a “hydrogel” material that swells when it is warmed and contracts as it cools. Mid president Marthinus van Schoor says the hydrogel-neoprene suit, developed for the U.S. Navy Seals, hugs the diver in cold seas, reducing the amount any water trapped inside the suit sloshes across the skin and carries away heat; in tests at 13 C, hydrogel-impregnated suits provided 70 percent more thermal protection than neoprene alone. Santa Cruz, CA-based wet suit manufacturer O’Neill plans to test the Mid technology. If it passes muster, divers won’t be left shivering for much longer.