The heat lasts for a couple of hours !!!!
I was very happy with the way the hot pack heated up. The belt makes it very easy to keep it around your back and keep doing what you have to do. After you have used it and want to break it down again for the next time you need it, I recommend that you boil the water then take the pot off the burner.  Let it melt the gel. I put it in while the water was at a full boil and kept it boiling. When I went to take it out with a spatula it leaked.  It was quite a mess. I contacted the seller to get a replacement gel pack.  They sent me one at no charge.  The customer service of this company was the best.
Rating: 4 stars