We are using the bags (I like the bags) and we have a heater, don't let anyone tell you you don't need a heater even if the room is 85. We have forgotten to turn the heater on and my husband was sooooo cold his teeth were chattering, we had 2 blankets on him and wamers you stick in the microwave. If no heater find a way to warm up. I kinda like the warm water idea.