Phase-change materials keep astronauts warm in the black void of space and cool in the solar glare. Microencapsulation is the bane of scent-sensitive magazine readers. Now two companies-Outlast Technologies, based in Boulder, Colo., and Frisby Technologies, based in Freeport, N.Y.-have married these technologies to create new kinds of clothing that regulate the wearer's body heat.

Phase-change materials store or release heat as they oscillate between solid and liquid form. As a phase-change material changes to a solid state, it gives off heat; as it returns to a liquid state, it absorbs it-like a melting ice cube drawing the heat from a glass of water. In fact, water can be defined as a phase-change material with a trigger temperature of 32 degrees Fahrenheit. Such materials are common; one NASA study identified more than 100.