This heat pad is great for keeping you warm in the cold weather. To activate the heat pack simply press and pop the small disc inside. The heat pack then crystalises and generates instant heat for up to 30 minutes. To re-use put the hardened heat pack into boiling water and boil for 5-10 minutes until the crystals have dissolved. Once the pack has fully cooled down, you may reuse at any time. Perfect for camping, outdoor & sports activities.