Phase change material compound and pack

A phase change material incorporates a conductive compound which comprises carbon black particles. The PCM may be a salt-based material e.g. sodium sulphate decahydrate or paraffin. Other agents may also be included e.g. lithium fluoride, clay mineral, xanthan gum. Also shown is a PCM (phase change material) pack which comprises an envelope of relatively highly thermally conductive material enclosing a portion formed primarily of PCM; wherein said PCM portion incorporates a conductive compound mixed into said PCM which comprises carbon black particles.