Heatpacks by Uniheat are the perfect solution when shipping perishable items and live goods. Used commonly within the aquarium hobby, these heat packs are great for ensuring that your aquatic plants, aquarium fish and more stay warm and safe during transit. The Uniheat Heatpacks warm up quickly and are ready to use within 3-5 minutes of simply opening the package. They do not require any shaking or kneading and last for the time advertised. One heat pack warms up substantially and can increase the temperature around 20 degrees Fahrenheit in a 1cu. ft. box. For each additional heat pack added, the temperature raises in 10-degree increments. These heat packs by Uniheat are also eco-friendly and their contents are biodegradable. Perfect for those who live in colder areas, these heat packs by Uniheat are available in 40 hours and 72-hour packs. NOTE: When adding to cart, please specify if you would like us to activate the heat pack for your order, or if you would like it unopened. If no note is added, the heat pack will be used.