Don't be tempted to skimp on carpet padding to save a few dollars. Just as a building needs a solid foundation, carpeting relies on a layer of padding for support, strength and a bit of extra cushioning. You can't see the padding, but you'll definitely spot the extra wear and tear on your new carpet if you pick an inadequate padding material.
Made from rubber or foam materials, carpet padding conceals subfloor imperfections to improve the appearance of the finished floor. It also acts as insulation to help control the temperature of your home, and it even absorbs sound to protect your privacy and eliminate neighbor noise. Most importantly, padding supports your carpet through years of use, since it prevents carpet backing and fibers from coming apart over time.
Consult your carpet manufacturer for padding recommendations and advice. Typically, high-traffic areas require firm, dense padding, while guest bedrooms and other light-traffic rooms may need less protection.
It's also important to match the padding to the type of carpet you plan to use. The Carpet and Rug Institute recommends a 7/16-inch (11-millimeter) padding with 6 pounds (2.7 kilograms) of density per cubic feet to support cut pile or cut loop carpeting. For Berber or thin loop rugs, look for a 3/8-inch (9.5-millimeter) pad or thinner, with 8 pounds (3.6 kilograms) of density per cubic foot [source: Carpet and Rug Institute].