There are 2 types of rug pad.

The felt and rubber pad is a 1/4” thick compressed felt with a rubber back.  On a hard floor, use the pad with the rubber side down, facing the floor.  Over wall-to-wall carpet, use the pad with the felt side down, facing the floor.  This is the highest quality pad of its type, providing both cushioning and non-skid properties.

The thin rubber pad is approximately 1/8” thick.  This pad is solid rubber, reinforced with nylon thread.  It is used under rugs when the customer wants a non-skid product that has a slim profile.  Buy the thin rubber pad when you are concerned about using the rug near a doorway that has a low clearance.