Underlayment is the thin spongy material that carpet layers put under carpet. Usually it’s called padding or cushion but underlayment is the industry term . They can be used for any number of things: they make walking on them easier on the feet, they can absorb sounds so people upstairs cannot hear you walking.
Padding your carpet will protect your carpet from wearing down, and it’s not difficult to see why. Constant foot traffic mashing directly on the carpet and the floor simply breaks the backing.
When you buy padding, it should be about as thick as the carpet itself. A berber carpet with a thick padding will be too springy. Likewise a thin cushion under a shag carpet will be ineffective. Padding density ranges from 6 pounds / cubic foot for residential carpets and 8 pounds / cubic foot for commercial carpets.
As a rule, you should not use underlayment on commercial carpet, except for the reasons mentioned above. For instance you might want padding in a lobby. Also if you have employees who are on their feet all day, like in a department store, you might think about padding. Also note that commercial carpet padding is entirely different from residential padding, and if you have it installed, make sure you’re getting the right one.
Written by, Derek Beyer.