Bought separately from the carpet, priced by the square foot, and specified by density — not the thickness printed on the sample. Get that backward and the mistake stays invisible for years, then quietly voids a warranty on carpet that was otherwise fine.
It is the one thing almost every buyer gets wrong. Density carries the load; thickness only feels good for the moment you stand on the sample. The Carpet and Rug Institute puts residential cushion at no more than 7/16 inch, and mill warranties on cut-pile carpet generally set the same ceiling alongside a minimum density of 6 lb/ft³.
Exceed the thickness and the carpet backing flexes over the cushion with every footstep until it breaks — so the upgrade shortens the life of the carpet and voids the warranty that would have covered it.
Bought by the square foot alongside the carpet, and specified by density in pounds per cubic foot. If a quote lists a thickness and no density, that is the question to ask.
6–10 lb/ft³ · 3/8″–7/16″ · $0.50–$0.90/sq ft installed
Shredded scrap foam bonded into a sheet — the multicolored pad in almost every home in America. It is the default for good reason: at 8 lb density it meets nearly every mill warranty and costs a fraction of anything better.
Use it for: Cut-pile carpet in bedrooms, living rooms and hallways.
Watch out: Below 6 lb it fails early and voids most warranties. Retailers quote pad by thickness because it sounds like value; ask for the density in pounds.
2–4 lb/ft³ · 7/16″–1/2″ · $0.30–$0.50/sq ft installed
Virgin foam, not bonded scrap. Feels luxurious in the showroom because it is soft and thick, and that is exactly the problem.
Use it for: Light-traffic rooms on a tight budget, and not much else.
Watch out: Bottoms out under traffic within a couple of years, and its density is usually below the minimum the carpet warranty requires. The classic builder-grade pad.
12–20 lb/ft³ · 1/4″–3/8″ · $1.20–$2.00/sq ft installed
Chemically frothed rather than shredded and glued, producing a dense, uniform pad that is thin and firm rather than thick and soft.
Use it for: The upgrade worth paying for. Long-run hallways, stairs, and any carpet you want to outlive its warranty.
Watch out: Feels harder underfoot in the showroom than a cheap thick pad, which is why it loses the sale. It is the pad that keeps the carpet alive.
18–22 lb/ft³ · 1/4″–3/8″ · $1.50–$2.50/sq ft installed
Dense flat sheet rubber. The firmest common cushion and the longest-lived — frequently outlasts two carpets.
Use it for: Heavy traffic, stairs, commercial and institutional work, and rolling loads.
Watch out: Expensive, heavy to handle, and unnecessary in a bedroom. Do not confuse it with waffle rubber, which is a different product.
Hollow-domed sheet · $0.60–$1.10/sq ft installed
Rubber molded with hollow air domes so it feels soft for its weight. Largely superseded by rebond and frothed urethane.
Use it for: Rarely specified new. You will meet it lifting an old floor.
Watch out: The domes collapse and the pad takes a permanent impression of the traffic pattern. Not a current recommendation.
Jute, hair or synthetic · firm · $0.60–$1.00/sq ft installed
Needle-punched natural or synthetic fiber. Firm, dense, and almost incompressible compared with foam.
Use it for: Berber and other loop constructions, patterned carpet, and over radiant heat where foam insulates too well.
Watch out: The right answer for loop carpet specifically — a soft pad lets the backing flex, and flexing is what breaks loop backings.
8–10 lb/ft³ + bonded film · 3/8″–7/16″ · $0.90–$1.40/sq ft installed
Standard rebond with an impermeable film bonded to the top face, so liquid stops at the pad instead of passing into the cushion and the subfloor. Some are sold with an added pet-urine treatment on top of the barrier.
Use it for: Households with animals or small children. The single most useful cushion upgrade a pet owner can buy.
Watch out: It stops liquid reaching the subfloor, not the carpet — the carpet still has to be cleaned, and quickly. Breathable versions block liquid while still letting vapor escape, which matters over a slab.
10 lb/ft³ slab + barrier · 3/8″–7/16″ · $1.50–$2.20/sq ft installed
Dense slab rubber with an integral barrier. The most durable moisture-resistant cushion made, and the only one that will comfortably outlive the carpet on top of it.
Use it for: Below-grade rooms, concrete subfloors, and pet households where the carpet will be replaced before the pad is.
Watch out: Roughly triple the price of plain rebond. Justified over a slab or with animals; hard to justify in a spare bedroom.
Density is what a quote leaves out and thickness is what it advertises. This is the number to ask for.
| Density | What it is | Where it belongs | Note |
|---|---|---|---|
| 6 lb/ft³ | The floor, not a target | Guest rooms and light-traffic bedrooms. | The minimum most mill warranties on cut pile will accept. It works, and it will not last as long as 8. |
| 8 lb/ft³ Default | The residential default | Living rooms, bedrooms, hallways — most of a house. | At 7/16 inch this is the configuration that satisfies essentially every warranty. If a quote does not state a density, this is what to ask for. |
| 10 lb/ft³ | Traffic and stairs | Stairs, long hallways, and any run that gets walked every day. | Stairs in particular want density rather than softness — a soft pad on a nosing wears the carpet through at the edge. |
| 12–22 lb/ft³ | Frothed urethane and slab rubber | Commercial work, rolling loads, and carpet you intend to keep. | Thin and firm rather than thick and soft, which is why it loses the showroom comparison and wins over ten years. |
No, and this is the most expensive misunderstanding in a carpet showroom. Density carries the load; thickness just feels good underfoot for the thirty seconds you stand on the sample. The Carpet and Rug Institute puts residential cushion at no more than 7/16 inch, and most mill warranties on cut-pile carpet set the same ceiling with a minimum density of 6 lb/ft³. Go thicker and the carpet backing flexes over the cushion every time someone walks on it, which breaks the backing from underneath — so the pad that felt like an upgrade shortens the life of the carpet and voids the warranty at the same time.
Eight pounds per cubic foot of bonded urethane at 7/16 inch is the residential default and satisfies essentially every mill warranty. Six pounds is the floor, not a target. If you want to spend more, spend it on density rather than thickness — a 1/4 inch frothed urethane at 15 lb outperforms a 1/2 inch prime foam at 3 lb by every measure that matters, including how it feels after two years.
More than most upgrades. Standard cushion passes urine straight through into the subfloor, which is where the smell lives and why the smell survives cleaning the carpet. Moisture-barrier cushion bonds an impermeable film to the top of standard rebond so liquid stops at the pad. It does not clean the carpet for you, and it is only as good as its seams, but it keeps the problem in a layer you can replace.