In normal circumstances, heat will flow through the garment to the outer environment. With the presence of PCMs within the garment, this flow is interrupted as the PCM absorbs or releases the heatpreventing the heat access to the outer environment. In this way an active thermal barrier (insulation) is created that is in addition to the normal passive thermal barrier inherent in the garments design.

Burlington Worldwide (BWW), in partnership with Outlast Technologies and Ciba, has created a finish that allows fabrics to adjust to changes in temperature for more comfortable and versatile clothing. The patent-pending technology, called Smart Fabric Technology, is built around micro encapsulated phase-change materials called Thermocules. These materials absorb and release heat for increased comfort without compromising the fabric's inherent characteristics. A paraffin-PCM, for example, absorbs approximately 200 kilojoules per kilogram of heat to undergo a melting process. This high amount of heat absorbed by the paraffin in the melting process is released into the surrounding area during the cooling process starting at its crystallization temperature. During the complete melting process, the temperature of the PCM as well as its surrounding area remains constant. The excess heat generated by a body in action is absorbed by the paraffin in the PCM which melts in the process and stores the heat. Since the excess heat has been taken away from the body, the undesired temperature increase concomitant with the normal heating process does not occur. The same is true for the crystallization process. During the entire crystallization process the temperature of the PCM does not change either. The high heat transfer during the melting process as well as the crystallization process without temperature change makes PCM interesting as a source of heat storage.

The PCM is normally present in microcapsules, which can resist wear and tear during the life of the garment. Microencapsulated PCMs can either be distributed within fibers or coated onto the fabric. Whilst the concept of using PCMs is clearly a very attractive one, there are still a number of limitations. Acrylic is the only commercially available fiber that is compatible with PCMs, and there is an upper limit to the amount of PCM that can be incorporated in the fibers before tensile properties are appreciably reduced. Where PCMs have been coated onto fabrics, fabric hand may be compromised, and durability to abrasion during wear and to washing and dry-cleaning may be lowered.

The selection and incorporation of PCMs in textiles requires care. The most important consideration is the actual temperature of the phase change, and in garments this should normally be 30-35 C, close to the bodys temperature. Other key factors include cost, toxicity and availability. The initial applications of the finish will be in fabrics for active wear apparel. Future planned applications include men swear, uniform and barrier products.