What type of cushion/ pad should I use under my carpet?

That is up to you! Lowe's offers a wide variety of padding from the basic "Super6" pad to the ultra soft "Stainmaster Elite Foam" pad and everything in between. New pad is nice to walk on, clean, free of residual odors, and increases the life of your new carpet. Your Lowe's flooring specialist can help you choose the best pad to go with the type of carpet you select. Carpet manufacturers have recommendations for cushion specifications. Cut pile carpet should have a firm cushion that is no thicker than 7/16 of an inch. Berber carpet and most commercial carpet should have a very firm cushion no thicker than 3/8 of an inch.