These are rechargeable heat pads that you can use time and again. Click the small metal disk inside the pads and they instantly heat up to 54°C. Each activation will give heat for up to 40 minutes (great for boiling eggs). To recharge the pads simply boil them for 5 minutes and allow to cool and they'll be ready to go again. Pack of 2 pads measuring 9cm x 9cm.