NNT or cold pad with inner element

A flexible heat transfer device for heating or cooling a surface such as the skin has an envelope formed from two sheets. The envelope contains a high thermal capacity first material such as a freezing gel that is flexible when frozen for good surface contact, A pouch within the envelope contains a high thermal capacity second material that may have different physical properties than the first material. The pouch may be segmented, or there may be multiple pouches. The device is more versatile in its applications and provides for more prolonged heating and cooling, The pouch may be in two parts within a frangible partition that generates heat or cold when the partition is ruptured and the two parts mixed.