Like the cushion under wall to wall carpets, a good rug pad helps protect the area rug from wear and tear by absorbing the majority of the impact from foot traffic. A rug pad provides a protective barrier between the area rug and the floor underneath. They prevent scuffs and scratches from the rough backings of some area rugs when and if they shift from foot traffic.
Nonskid Area Rug Cushion
The best underlayment w/ an IIC of 70 and a Delta IIC of 28
Why stock multiple underlayments when you can stock one product for all your hard surface installs.