This unique hand warmer is referred to as crystallization type because it is activated by flexing a small metal disk inside the hand warmer that will product heat. Will stay warm for 15-25 minutes. Simply immerse in very hot water until contents become fluid and allow to cool. Can be used up to 300 times. Instructions are printed on items. 3.875" Diameter x 0.5" W. Price includes 1 colour; 1 location imprint.