Does carpet pad quality really matter?

What the layer underneath is actually doing

Carpet is a textile. Laid straight onto a subfloor it has almost no ability to absorb an impact, and it was never built to have any. Every step you take compresses the pile first, and once the pile has compressed, the load arrives at the backing, which is the woven layer the tufts are locked into. The cushion exists so that the backing does not have to take that load against something hard.

Picture the same footfall twice. On a correct cushion, the pad compresses, the energy spreads out across a wider area, and the backing barely moves. On a worn out or badly matched cushion, the backing takes the hit almost directly against plywood or concrete, flexing at that one spot, over and over, in the same narrow walkway. Backing worked that way eventually loosens its grip on the tufts it is holding. Carpet rarely wears out from the top down. It comes apart from the bottom up, and the lane people walk is where you find out.

Density carries the load, thickness gives the feel

Two specifications describe a cushion and they do completely different jobs. Density is how much material is packed into it, and density is what carries weight without bottoming out. Thickness is how far the cushion travels under a foot, which is most of what you feel when you stand on it. They are independent of each other. A thick soft cushion and a thin dense one are not two points on the same scale.

One thing worth being blunt about, because the vocabulary collides. This is the cushion's own density, a property of the foam or fiber itself. It is a different specification from the density of the carpet on top of it, which is face weight read against pile height. The two get discussed in the same conversation constantly. A dense carpet sitting on a soft cushion is still sitting on a soft cushion.

Why too soft is the real mistake

The instinct is that a softer cushion must be a kinder one. It is not, and this is the single most useful thing to understand about pad. On a cushion too soft or too thick for the carpet above it, the floor starts behaving a little like a trampoline. Each step lets the carpet drop further than its backing was designed to travel, then spring back. Across a walkway that is a flexing cycle repeated constantly, and it works the backing loose, puts stress into the seams where two pieces were joined, and lets the carpet move enough at the edges to show it.

This is why most carpet warranties name a cushion specification at all, a point the carpet page covers. The cushion is not chosen to be as plush as possible. It is chosen to match the carpet and the room.

Stairs are where it matters most in the whole house. A stair nose carries the entire weight of a step on one edge of one tread. A soft cushion lets the carpet roll over that edge under the load, so the nosings wear out first and a staircase ends up looking finished at the treads and tired at every edge. Stairs want a firm cushion, and the rest of what a stair asks for is in the stair answer.

The constructions, and the jobs they suit

• Bonded urethane. The flecked, multicolored cushion most people picture, made from reclaimed foam bonded into a slab. It covers most rooms in most houses, and it comes in a wide range of densities, which is where the actual decision sits.
• Firm slab foam and rubber. Denser, with less travel underfoot. The right answer for heavy traffic, for a room with a rolling chair, and on a staircase.
• Fiber cushion. Felted synthetic or natural fiber, firm with very little give. Usual under loop and Berber constructions and in commercial rooms, where a springy floor is the wrong feel and the wrong mechanics.
• Memory and frothed foam. Built around how it feels standing still. At home in a bedroom, where comfort is the job and traffic is not.
• Moisture barrier. A thin film laminated to the top of a cushion so a spill or an accident stops there instead of soaking down into the cushion core and the subfloor. Anything that gets that far is what a room still smells of long afterward, which is why it comes up on carpet for pets.

Sound, cold and the subfloor underneath

The cushion does three more things that have nothing to do with how long the carpet lasts. The first is quiet. Most of what a carpeted room gains in silence it gains from the cushion rather than from the carpet, which is why the same carpet can sound different over two different pads.

The second is cold. A cushion is a layer of trapped air, and over a slab, an unheated crawlspace or a finished basement, that is most of what you feel through a sock in February. The third is telegraphing. A subfloor is rarely perfect, and a cushion of the right density bridges minor irregularities so they do not read through the carpet as shadows. It will not fix a subfloor that has a real problem, and that gets found at the in-home measure rather than after the carpet is down.

Where the cushion decision gets made

Pad gets chosen with the carpet, not after it. A firm cushion under a dense carpet on a stair, a plusher one under a deep pile in a bedroom, a moisture barrier where animals live: those are decisions made together, because the pairing is what performs and neither half performs alone.

Whether existing cushion can stay has its own page, reusing old pad. How the pieces of a carpet job come together on a quote is a separate subject and lives on carpet cost factors. What a particular carpet calls for underneath it is printed on its own spec sheet, and we will read that with you at the Wentzville showroom. Call 636-332-0654.