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, Stays 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. Complies with CPSIA, Prop 65. 0.5" H x 3.875" Diameter. Price includes a 1 Colour Imprint. Imprint area is 1.75" W x 1.125" H on Front. Call for multi-colour or multi-location imprints or for rush delivery availability.