Phase change material. Coloured scanning electron micrograph (SEM) of microcapsules (blue) that contain a phase change material (PCM) coating fabric fibres. The PCM can absorb and release heat generated by a person wearing the fabric, warming or cooling it as required. If the wearer's body temperature rises after exercise, the PCM absorbs the heat and melts, preventing heat reflecting back onto the body. If the wearer's temperature then falls, the PCM refreezes, releasing its absorbed heat and warming the garment. The PCM can undergo this melting/refreezing cycle almost indefinitely. PCMs are being developed by Outlast Technologies, USA. Magnification unknown.