SO EASY TO USE: The principle is simple. To activate the wallet, immerse it in cold water for 10-15 minutes. Crystals contained in the panels of the wallet then expand into a gel, which remains cool for several days - relying on the process of evaporation for cooling. Then just towel dry the outside and it's ready to go! SIZE: 6x4 inches SPECIAL FEATURES: Although activated by water, a feature of the product is that after towel-drying, the FRIO wallet is dry to the touch. The Cambrelle pouch we supply free of charge with each FRIO cooling wallet increases the wallet's efficiency and allows it to be carried safely in your pocket or a bag as required. Each item is re-usable and can be used either continuously or intermittently COMPATIBILITY: Designed to suit all types and makes of insulin pens and standard refill cartridges.