Set of 2. 
 
To activate: find the round metal disc and firmly flex. The gel will turn white and rapidly heat up.
 
To reactivate: once the product has cooled down and hardened, cover it with a cloth and submerge in a pan of cold water. Bring to the boil and simmer for around 5 minutes until the gel becomes clear. Allow the water to cool before removing the product. Before reactivating make sure the product is cold.