Microcore Heat Packs are microwaved and placed inside of a REVO Dubler cooler, making it a flameless chafer. Place microwaved heat packs in cooler then hot food trays and cover with lids. The combination of the hot trays, heat packs and premium insulation keeps food warm for hours. 2 Microcore Heat Packs are included in every Dubler HEAT. Extra Microcore Heat Packs are sold as a set of 2. Instructions: Microwave heat packs until they begin to swell then quickly stop heating. (Could be 2 to 5 minutes depending on strength of microwave.) Over swelling can cause a leak. They are not warrantied for that. Be careful handling the heated pack. The contents (cellulose sponge and water) are not toxic.