I use them for the kittens and puppies that I foster for our local shelter. They do hold heat for quite a while (and the individual disks hold up pretty well if you are careful and don't overheat them -- I have had mine for five years or so), but they don't radiate heat so much. The animal has to really be standing or sitting on it (or up next to it?) to benefit from the warmth. When I have kittens, I usually heat one up around 9:30 pm for them, and it is still slightly warm at around 7 in the morning -- this is indoors, usually in a cooler room, on a tile floor, so I am not sure how it would go outdoors. It comes with a cover, but I have also wrapped them in tea towels which are a little thinner; you could make your own covers or pockets to prevent unintentional burns, as they start out very hot.