10 Pack Pack of unique warmers are designed especially for shipping plants, reptiles, fish and corals. Wholesale exporters use them worldwide for shipping plant, reptile and fish. The Uni-Heat Warmer will warm up and is ready to use within 5-15 minute of being exposed to the air. One heat pack will increase the temperature of a 1cu. ft. box by 20 degrees, for every additional heat pack that you use the temperature, will raise an additional 10 degrees. Each heat pack will last more than 72 hours and is environmentally safe, disposable and the inner contents are biodegradable.