If you use it to warm your feet by putting it on the floor and having socks on, resting your feet on it but changing position because of the heat, around one ho

If you use it to warm your feet by putting it on the floor and having socks on, resting your feet on it but changing position because of the heat, around one hour, a bit more. If you use it to have something warm in your bed, if you leave it below the blanket it will still be warm in the morning. But putting it with boiling water in the bed means that you just can't touch it because it's really hot. You may put your feet on it for 10 to 20 seconds or put it on your stomach for the same amount of time, to heat up quick, but then you need to place it somewhere where it has no direct contact with you. I just love mine, which is one made of flexible rubber (or pvc). When I get up I start making my coffee and in parallel I heat up a kettle of water until it boils, then i use that one under the desktop for my feet. Sometimes I put it on my lap or hug it for a while. It's worth it, but only during the winter.