HOT RODS® Warming Packs are air-activated, time release warmers that stay active for hours! Hot Rods literally "run on air". Each soft, lightweight pouch contains a mixture of iron powder, water, vermiculite, cellulose, activated carbon and salt. Once the outer package is opened, an oxidation process takes place which causes a safe, natural reaction to release heat. HOT RODS® warming packs utilize the same technology as used by the National Ski Patrol, explorers of the Arctic and Antarctic and military forces. If warming time is not completely exhausted, HOT RODS warming action can be preserved for several days by packing them in an airtight container, such as a zip-seal poly bag.