This dense 18mm thick underlay is made from recycled rubber finished in a hessian matting to allow your putting grass to stick to. Its used for a number of different benefits, 1) If your floor has no insulation, this helps keep cold out. 2) If your floor is uneven, helps allow the ball to run smoother when putting on top. 3) If your room is attached or inside your home helps massively with sound dampening. 4) If you want to fit your driving mat to sit flush with your putting grass (30mm thick V 12mm thick) it allows you to cut out an area the size of your mat and set it down into the formed well.