Before I bought a temperature controlled propagation mat, I used to use an electric back warmer, the kind for sore back muscles or whatever hurts. I got the ones designed so that you can get them wet for "moist heat". They are usually about 12 inches by 24 inches so they are just about right for one seed flat. They have three heat settings, low, medium, and high. The medium setting was just about right. I don't know how safe it is to use these for seed germination, but since they are designed to get wet I think they OK as long as you don't put anything sharp or heavy on them. Mike Benson