A memory foam mattress topper is the quickest way to change how your bed feels without changing the bed. Done right, it adds contouring pressure relief to a mattress that is too firm or has simply lost its plushness. Done wrong, it is a hot slab of foam hiding a problem that needed a different fix.
Quick answer: A memory foam topper suits you if your mattress is structurally sound but too firm, or has lost its surface comfort. Around 4cm of open-cell memory foam with a breathable cover is the sweet spot: enough depth for genuine pressure relief without the sunken, overheated feel of very thick foam. What a topper cannot do is rescue a sagging mattress: foam laid over a dip follows the dip.
What a memory foam topper actually does
The foam softens with body heat and pressure, moulding to your shape so your weight spreads across the surface instead of concentrating at the shoulders and hips. On a firm mattress, that turns a hard surface into a cushioned one while the support underneath keeps doing its job.
Three jobs it does well:
Softening a too-firm mattress. If your mattress supports you properly but feels harsh at the pressure points, a topper fixes exactly that, and is far cheaper than replacing a mattress that is otherwise right.
Reviving a tired but sound surface. When the comfort layer of an ageing mattress has compressed but the core is still supportive and flat, a topper restores the plushness.
Protecting a new mattress's feel. A washable-cover topper takes the nightly compression, keeping the mattress surface fresher for longer.
What it cannot do
A topper is a comfort layer, not a support layer. If your mattress dips visibly, creaks, or leaves you rolling toward the middle, foam on top will follow every contour of the problem underneath. The same goes for a mattress causing back pain through lack of support: softer on top does not mean better supported.
Our guide on whether you need a mattress topper walks through that decision honestly, and if the mattress itself is past it, how often you should replace your mattress covers the signs.
How thick should a memory foam topper be?
| Thickness | What it feels like | Verdict |
|---|---|---|
| 2 to 3cm | A subtle surface change that bottoms out under hips and shoulders | Too thin for real pressure relief on most builds |
| 4cm | Genuine contouring without deep sink, and the mattress support still comes through | The sweet spot for most sleepers |
| 6 to 8cm | A dramatically softer bed with a sunk-in feel, harder to move on, warmer | Only for sleepers deliberately chasing a very soft feel |
Deeper is not better. The thicker the foam, the more you sink into it, the harder repositioning becomes, and the more heat gathers around you. Thickness should change the surface, not swallow the sleeper.
The heat question, answered properly
Memory foam's classic weakness is warmth: dense foam holds body heat exactly where you are lying. That matters for sleep quality, because your body needs to shed heat overnight, and the Sleep Foundation puts the ideal bedroom at around 18°C.
The fix is construction, not a thinner duvet. Open-cell foam lets air move through the material instead of trapping it, and a breathable or mesh-bordered cover gives that warm air somewhere to go. If you already sleep warm, treat these two features as non-negotiable in any topper you consider: this is what separates a cooling mattress topper from an ordinary foam one.
Our pick: the REM-Fit Halo
The REM-Fit Halo Memory Foam Topper is built to exactly this recipe: 4cm of open-cell visco memory foam for contouring pressure relief, under a Re-Ax cover with a mesh border that keeps air moving. Expert Reviews named it their Best Cooling Topper. Elastic straps and an anti-slip base hold it in place, and the cover unzips for machine washing.
REM-Fit Halo Memory Foam Topper
Expert Reviews Best Cooling Topper: 4cm of open-cell visco memory foam with a breathable Re-Ax cover, anti-slip base and machine washable cover.
Shop the Halo Topper✓ 30-night trial (100 when bundled with a mattress) ✓ 10-year guarantee ✓ Free UK delivery
Memory foam vs other topper fillings
Feather and down toppers feel cloud-like on night one, then compress into lumps that need daily shaking out. They add softness but no pressure relief, because they offer no resistance.
Microfibre and polyester toppers are the budget option: a plump quilted layer that flattens within months and slides around the bed.
Memory foam is the only common topper filling that actually redistributes weight rather than just padding the surface, and the only one that returns to shape every night for years. That is why it dominates the category, and why the heat question above is worth getting right rather than avoiding the material.
Looking after a foam topper
The rules match memory foam pillows: wash the removable cover, never the foam itself, and air the topper when you change the bedding. Rotate it head to toe every few weeks so compression spreads evenly, and let it expand fully for a few hours when it first arrives. While the bed is stripped, it is the perfect moment to give the mattress underneath a proper clean too: our guide to cleaning a mattress covers it step by step.
Frequently asked questions
Do memory foam mattress toppers really work?
Yes, for the right problem. On a firm or surface-tired mattress they add genuine contouring and pressure relief, which is why side sleepers and anyone with pressure-point aches feel the difference first. They do not add support, so they cannot fix a sagging or unsupportive mattress.
How thick should a memory foam topper be?
Around 4cm suits most sleepers: enough foam to contour properly without the sunken, hard-to-move-on feel of thicker slabs. Go thicker only if you deliberately want a much softer bed, and thinner only if you need the mildest surface change.
Can a topper fix a sagging mattress?
No. Foam follows the surface it lies on, so a topper over a dip becomes a dipped topper. If your mattress has visible sag or you wake up rolled toward the middle, the mattress needs replacing, and any topper budget is better put toward that.
Do memory foam toppers make you hot?
Traditional dense foam can. Open-cell foam with a breathable cover largely solves it, because air moves through the material instead of being trapped against your body. If you sleep hot, make open-cell construction and a breathable cover your two filters.
How do you keep a mattress topper in place?
Straps and grip. Look for corner or edge straps that anchor to the mattress and an anti-slip underside, then fit your sheet over both mattress and topper together so the whole surface moves as one.
