There’s a continuous flow of air through a permeable felt mat. The fabric (or cardboard, or plastic or whatever) doesn’t get stuck like with a suction cup, it’s

There’s a continuous flow of air through a permeable felt mat. The fabric (or cardboard, or plastic or whatever) doesn’t get stuck like with a suction cup, it’s more like how a vacuum cleaner will pull fabric and it’s difficult to remove. The machine makes a lot of noise when it’s running, due to this suction.