How to Choose a Memory Foam Mattress Topper

Updated 3 October 2026 · 4 min read · 7 sections

A mattress topper is the cheapest way to change how a bed feels. It only works when thickness, foam density and cover design are matched to what is actually wrong with the mattress underneath.

What a topper can and cannot fix

A topper changes three things: surface softness, pressure relief at the shoulders and hips, and airflow directly under your body. It cannot fix a sagging core, a broken spring unit, or a bed frame that flexes. If the mattress has lost its structure, a topper follows the sag instead of hiding it.

A topper is the right purchase when:

• the mattress is structurally sound but sits too firm;
• you need pressure relief at the shoulder or hip, and the mattress is otherwise fine;
• two people want different surface firmness on the same bed;
• you want to extend a mattress that is several years old but has not failed.

If the mattress dips by more than roughly 1.5 inches at the middle while you lie on it, replace the mattress. No topper compensates for that.

Thickness: 2, 3 or 4 inches

Thickness is the strongest single lever on how much a topper changes the feel of a bed.

• 2 inches adds surface softness and shifts the mattress feel only slightly. It suits a mattress that is marginally too firm, and guest beds where the topper is stored between visits. It rarely changes pressure points in a meaningful way.
• 3 inches is the everyday middle. There is enough foam to relieve shoulders and hips for most side and back sleepers without turning a firm mattress into something you sink into. Most buyers should start here.
• 4 inches is for a genuinely hard mattress, or a heavier sleeper who sinks through thinner foam to the mattress below. It adds the most height to the bed – and the most warmth.

Density predicts lifespan better than the word firm

Foam density is measured in pounds per cubic foot (lb/ft3). Retail listings rarely print it, but it is the best available predictor of how long a topper holds its shape.

• Under 3 lb/ft3 – budget foam. It feels fine for a few months, then flattens where you lie. Avoid if you expect two years of use.
• 3 to 4 lb/ft3 – the practical band for a topper that keeps its shape for roughly two to four years.
• Above 4 lb/ft3 – denser, heavier, more supportive, and noticeably warmer, because air moves through it less easily.

Firmer is not the same as denser. A dense topper can still feel soft. A low-density topper can feel firm on the first night and collapse within a season, which is why the two numbers have to be read together.

Gel-infused foam compared with plain memory foam

Plain memory foam responds to body heat: it softens where you are warm and slowly returns to shape when you move. That is what produces the pressure relief, and also what makes it sleep warm.

Gel infusion – beads, swirls or a graphite layer – is added to move heat away from the contact surface faster than foam alone. It reduces the heat build-up, but it does not eliminate it. If you already sleep hot, the more reliable fix is a thinner topper plus a breathable cover, rather than a thicker topper with a cooling label.

Which topper for which sleeping position

Cover, washability and lifespan

Memory foam itself should not be washed or soaked. Whatever keeps it clean is the cover, so the cover is not a cosmetic detail.

• Removable and machine washable is the feature worth paying for. Washing the cover monthly controls dust build-up and odour.
• Zipped, with the foam fully enclosed keeps the foam away from direct contact and slows the yellowing that comes with light and air exposure.
• No cover means the foam surface is the thing you sleep on. It will discolour, and it cannot be cleaned.

Expect a 3-inch topper in the 3 to 4 lb/ft3 range to feel noticeably less supportive after about three years of nightly use. Treat it as a replaceable layer, not a permanent part of the bed.

Decision checklist

1. Confirm the mattress is structurally sound. If it sags more than about 1.5 inches, a topper is the wrong purchase.
2. Pick thickness from the problem: 2 inches for mild firmness, 3 inches for pressure relief, 4 inches for a hard surface or a heavy sleeper.
3. Check the density figure, and treat any listing that omits it as a signalling problem.
4. Decide on cooling by construction, not by label. Thinner foam plus a breathable cover beats thick foam plus a cooling claim.
5. Require a removable, machine washable cover.

Related reading on this site: every NEWBULIG topper page lists its actual thickness, dimensions and cover construction in the Specifications tab, so the numbers above can be checked against the specific product rather than a category average.

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