I found out about a way to keep a hot compress hot longer.
Wet a washcloth, put it in a plastic baggie (leave it open) and microwave it for 60 seconds.
Seal the bag (be careful handling it; maybe use an oven mitt) and wrap the whole thing in a towel.
It stays VERY hot for the entire length of time you need to apply it, so you don't have to keep rewarming it.
Just be careful none of the hot water leaks out onto your skin. Learned that one the hard way.