Carpet padding serves three functions: cushions the carpet fiber against impact (footsteps compress the carpet against the padding — hard subfloor with no give crushes the fiber flat within months), extends carpet lifespan (proper padding absorbs the wear that would otherwise flatten and mat the carpet backing), and improves comfort underfoot and sound absorption.

The performance difference between quality padding and bargain padding is enormous. The same $4/sq ft carpet lasts 20 years over 8 lb padding and 10 years over 4 lb padding. The padding upgrade is typically $0.30-$0.60/sq ft — a fraction of the carpet cost and a huge impact on lifespan.

Padding density is measured in pounds per cubic foot. The number represents how much material is packed into a given volume — higher numbers mean denser, firmer padding. This is different from thickness. Two padding samples can both be 3/8″ thick, but one might be 5 lb density and the other 10 lb density.

Density is what matters for performance. A dense 3/8″ pad outperforms a fluffy 1/2″ pad because it doesn’t compress under foot traffic. Compressed padding stops cushioning the carpet fiber above it. Once compression is permanent (which happens quickly with low-density padding), the carpet’s wear layer is fighting hard subfloor with no protection — and it flattens fast.

Beyond density, there are three main padding material categories in residential use:

Rebond padding uses recycled foam scraps bonded into pads. It’s the dominant residential padding — colorful, dense, cost-effective, and works well when specified at 8-10 lb density. This is what you want under most residential carpet installations.

Prime foam is a single-piece foam pad without recycled content. Softer feel, less durable, and generally not the right choice for busy households. Common in very budget installations. Avoid for anything except rarely-used rooms.

Frothed foam / memory foam is a premium option with excellent sound absorption and comfort. More expensive, worth it for upstairs bedrooms and home offices where sound transmission matters.

Fiber pad is a specialty pad for Berber carpets — firmer than rebond to prevent Berber from getting “trampoline effect” that damages the carpet backing.

Most residential carpet warranties (Shaw, Mohawk, Karastan, etc.) specify a minimum padding density — typically 6-8 lb depending on the warranty tier. Installing over lighter padding technically voids the warranty, though claims are rarely disputed at that level.

Where it matters more: premium carpet warranties (25-year, lifetime residential) almost always require 8 lb minimum padding. Installing a premium carpet over a 6 lb builder pad is common practice among budget installers — and it silently voids the warranty you paid a premium to get.

Ask specifically: “What’s the minimum padding density required by this carpet’s warranty, and is your quoted padding at or above that minimum?” A good installer answers immediately with the specific spec.