I put a bag of frozen hamburger patties and some room-temperature groceries in this box-bag, after it had been in a very hot car (90+ outside) for six hours or so, so it was quite hot already. I drove home, stopping at another store for maybe a half hour, so all told, an hour, and the burgers were only slightly softened! Obviously, if the bag were kept in a shaded garage before a trip, or even better, in a climate-controlled house, the results would be better! Also, if there had been more frozenSee full review