The heat pack by itself takes approximately 1 hour to heat the QF bottle to 100 degrees. Thats why you should microwave the QF bottle for initial heat, then tape or band the heat pack to the back of the bottle. The heat pack wont take as long to heat up once its attached to the preheated QF bottle.

Once the heat pack is activated, it will keep the QF bottle at temp for 6-8 hours in a pocket of clothing.