Rebond - It is one of the cheapest pads, but durable enough to hold up for many years. Not ideal for excessively high foot traffic.
Rubber - Premium carpet, and very durable padding.
Solid foam - appeals more to the budget-conscious buyer. Ideal for low-traffic areas.
Memory foam - made of frothed foam with viscoelastic gel. Very comfortable to walk on, however, the foam can wear out over time.