Cold weather protective clothing of today consists primarily of many thin layers of insulating material. It would be far more desirable if cold weather protective clothing could release useful amounts of heat for periods of time during which the wearer's body was unable to provide sufficient heat to maintain body temperature. This approach is similar in concept to the use of phase change materials to store solar energy. The research explores the feasibility of producing fabrics which can store thermal energy through phase changes. If successful, this research would identify a new type of fabric for cold weather garments. These garments would be thinner than conventional garments, thereby allowing the wearer to work comfortably under cold weather conditions. Markets for this fabric include outdoor winter sportswear and winter emergency shelters and blankets.