Safe cooling without the risk of frost bite as with conventional cool packs. The moderate cooling temperature feels natural & provides a longer cooling time. The higher the outside temperature, the longer the high 37° version will stay cool compared to the lower 21° version. If you want a short intensive cooling & have access to a way to charge the lower 21° version, you better choose this version. Features Set of 3 pads Easy charging Modest temperature without risk of frostbite The 29° version will already charge at temperatures below 29° degrees & only starts cooling when it is really hot. The time to fully activate the cool packs depends on the coll pack temperature & the cooling method. In ice water it takes ca. 20 minutes, in a freezer ca. 40 min. & in a refrigerator ca. 60 min. Even storage below the specified temperature already charges the cool packs & it holds the temperature for hours. Lower than 19° C for the cool pack 21° Lower than 26° C for the cool pack 29° L...