Arctic Ice maintains lower temperatures longer than ice or "blue" ice substitutes. This cooler insert's reusable active ingredient, PureTemp is a non-toxic, biodegradable phase-change material (PCM) derived from plants. When Arctic Ice approaches its melting point (that's the phase change) it begins absorbing more heat while stubbornly refusing to warm up. It holds a constant, pre-defined temperature until the entire cooler pack finally thaws. The Alaskan Series freezes at 1 Degree Celsius (33.8 Degrees Fahrenheit) and efficiently keeps food and drinks chilled much longer than the same volume of ice. For optimal performance, freeze Alaskan packs in any household freezer for at least eight hours prior to use.