If you want the absolute best carpet underlay, choose flat rubber. While this underlay is more difficult to find and may be more expensive, it offers the longest life for carpet underlays. Many times this pad will outlive the original carpet.
With a in floor heating system, you have to have a different underlay. Look for one that is specifically designed for floor heating systems. Traditional underlay forms an insulating layer for your home that would trap the heat below the pad. This will interfere with the heating of the room and can create a dangerous situation with heat buildup. Look for a tog value of less than one for your carpet underlay.
