Guide · Sleep · 4 models
How to choose a mattress topper: depth, foam or fibre, the cover, and the UK bed sizes
Toppers are sold on a depth in centimetres and a word like memory foam or hollowfibre, and neither tells you whether the thing will fix your bed. This guide explains what depth actually buys, how foam and fibre differ in support, heat and lifespan, what to look for in the cover and the fixing, and the UK sizes, with four toppers from our shortlist as worked examples.
Start with the problem, not the product
A topper does one of three things. It can soften a mattress that is sound but too firm, which is a comfort problem. It can spread your weight across a mattress that has started to dip, which is a support problem and only a stopgap. Or it can give a good mattress a fresh, washable top, which is a hygiene problem. The depth and the material that solve one do not solve the others, so decide which you have before reading a single listing.
Lie on the bed on your back. If your hips and shoulders ache in the morning but the mattress is flat, it is too firm. If you can feel a hollow under your hips, or you and a partner roll towards the middle, it is dipping. If neither, and you just want the bed nicer, you want a pad.
Depth: what the centimetres buy
The depth figure is after the topper has expanded (foam ships vacuum-rolled and takes up to 72 hours) and before anyone has slept on it.
- 2 to 3 centimetres is a pad. It changes how the sheet feels, not how the bed supports you. The Silentnight Deep Sleep at 2.5 centimetres is the honest version of this: a quilted, washable layer with straps.
- 4 to 5 centimetres softens a firm mattress. In fibre it is plush at first and settles; in memory foam it is enough to take pressure off a side sleeper’s hips on a hard bed.
- 7 to 8 centimetres of foam in two layers is the first depth that changes support, because the firm base layer does the work and the memory foam on top does the comfort.
- 10 centimetres of fibre is plush rather than supportive, and compresses; it also lifts the bed enough that ordinary fitted sheets will not reach.
a pad: 2.5 cm, the lower limit of the word topper
Silentnight Deep Sleep Topper (double)
- Depth
- 2.5 cm†
- Fill
- Hypoallergenic hollowfibre†
- Cover
- Polycotton, quilted†
- Size
- Double, 135 × 190 cm†
- Fixing
- Elasticated corner straps†
- Washing
- Machine washable†
Check price on Amazon
The lower limit of the word: 2.5 centimetres of hollowfibre in a quilted polycotton cover, machine washable, corner straps. A padded protector, by the listing’s figures.
Strengths
- Cheap, light and washable
- Straps hold it like a fitted protector
Limitations
- 2.5 cm will not soften or support anything
- All figures from the listing
Good for
- a mattress protector with a little padding
- a child's bed
Look elsewhere if
- anyone shopping for comfort or support
Foam or fibre
Fibre, which Silentnight calls hollowfibre, is polyester fill like a duvet’s. It is soft, it breathes, it goes in the washing machine whole, it costs less, and it flattens where you lie. Silentnight sells its Airmax toppers with air-mesh side panels and a two-year guarantee, which is a fair description of what fibre promises: cool, washable, and not for ever.
a fibre topper: 5 cm hollowfibre, machine washable
Silentnight Airmax Topper 5 cm (double)
- Depth
- 5 cm†
- Fill
- Hollowfibre
- Cover
- Microfibre with air-mesh sides
- Size
- Double, 135 × 190 cm
- Fixing
- Elasticated corner straps
- Washing
- Machine washable
Check price on Amazon
Five centimetres of hollowfibre, box-stitched so the fill cannot migrate, mesh sides, elasticated straps, whole topper machine washable, two years’ guarantee. Silentnight’s page confirms the construction; the depth is the listing’s.
Memory foam is polyurethane that softens with body heat and moulds to you. It supports as well as cushions, it holds its shape for longer than fibre, and it is warm. The better toppers put a thinner layer of memory foam over a firmer support foam, so the sink is controlled and the base does the holding up. The cheaper ones are a single slab.
Strengths
- Machine washable, the whole topper
- Mesh sides for airflow on a hot sleeper's bed
- Two-year guarantee from a UK maker
Limitations
- Fibre flattens over time where you lie
- Depth figure is from the listing; Silentnight's pages vary
Good for
- a firm mattress that needs softening
- a guest bed
Look elsewhere if
- a sagging mattress, which needs foam
a two-layer foam topper: 3 cm memory foam over 5 cm support foam
Degrees of Comfort 8 cm Dual-Layer Topper (double)
- Depth
- 8 cm†
- Fill
- 3 cm gel memory foam + 5 cm support foam†
- Cover
- Knitted, removable, zip, airflow mesh sides†
- Size
- Double, 135 × 190 cm†
- Fixing
- Four corner straps and non-slip base†
- Washing
- Cover machine washable†
Check price on Amazon
Two layers: 3 centimetres of gel-infused memory foam over 5 centimetres of support foam, 8 in all, in a zip-off knitted cover with mesh sides, four corner straps and a non-slip base. This is the construction that bridges a dip.
Strengths
- 8 cm with a support layer, enough to change a firm or tired bed
- Removable washable cover, straps and a grippy base
Limitations
- Needs 48 to 72 hours to expand and air
- No maker page; listing facts only
Good for
- a firm or worn mattress that needs real softening
- side sleepers with sore hips
Look elsewhere if
- someone who sleeps hot and dislikes foam
a memory-foam-heavy topper: 5 cm over 2 cm
Uspark 7 cm Gel Memory Foam Topper (double)
- Depth
- 7 cm†
- Fill
- 5 cm gel memory foam + 2 cm support foam†
- Cover
- Bamboo-fibre and polyester (40/60), removable, zip†
- Size
- Double, 135 × 190 cm†
- Fixing
- Full-length elastic bands and non-slip base†
- Washing
- Cover machine washable†
Check price on Amazon
Memory foam first: 5 centimetres of it over 2 centimetres of support foam, a bamboo-blend zip cover, full-length bands and a non-slip base. More sink, less bridge; a side sleeper’s topper for a hard bed.
The rule: dip or pressure points, foam, two layers if you can. Too firm but flat and you sleep warm, fibre. Just want washable and nicer, a pad.
Strengths
- 5 cm of memory foam, the deepest comfort layer in this group
- Zip-off washable cover and full-length bands
Limitations
- Memory foam sleeps warmer than fibre
- No maker page; listing facts only
Good for
- a hard mattress and a side sleeper
- someone who likes the slow sink of memory foam
Look elsewhere if
- a hot sleeper
The cover, and what washable means
Fibre toppers wash whole: cover, fill and all, on a 40-degree cycle, and come out fluffed. Foam cannot be washed; what washes is the cover, which means you want a zip, ideally along three sides so the foam slides out, and a cover that is not so thin it tears on the way back in. Both foam toppers on our shortlist have zip covers; the Uspark’s is a bamboo-fibre and polyester blend, the Degrees of Comfort’s a knitted fabric with mesh sides.
Mesh side panels appear on fibre and foam toppers alike. They let the sides breathe; they do not cool the top you lie on.
Fixing: straps, bands or a skirt
A topper moves on a mattress unless it is held, and a 7-kilogram foam topper that has walked ten centimetres by Thursday is the most common complaint. Corner straps are the minimum and work on a fabric-topped mattress. Full-length bands, which run under the mattress across its width, hold better. A fitted skirt, like a sheet, holds best but only comes on thin pads. A non-slip base on the topper itself, a dotted or textured fabric, is worth having on a smooth mattress.
How to read a listing in five numbers
- Depth, and for foam, the split between memory foam and support foam. A single number for a foam topper usually means a single slab.
- Size, in centimetres. 135 by 190 is a UK double; 140 by 200 is not.
- Fill: hollowfibre, memory foam, or memory foam over support foam.
- Washing: whole topper or cover only.
- Fixing: corner straps, full-length bands, skirt, non-slip base.
If the listing gives a weight, it is a proxy for how much foam is in it; 6 to 7 kilograms for a double is a substantial foam topper, 1.5 kilograms is a fibre one.
UK bed sizes
| Name | Centimetres |
|---|---|
| Single | 90 × 190 |
| Small double | 120 × 190 |
| Double | 135 × 190 |
| King | 150 × 200 |
| Super king | 180 × 200 |
| EU double | 140 × 200 |
Silentnight’s pages quote 137 centimetres for a double in places; the straps absorb the difference. Buy the topper for the mattress size, not the bed frame.
Which kind, by bed
- Firm new mattress, sleeps hot: 5 centimetres of fibre.
- Firm mattress, side sleeper, sore hips: 5 to 7 centimetres of memory foam.
- Dipping mattress, replacing next year: 8 centimetres of foam in two layers.
- Good mattress, wants a washable top: a 2.5 to 3 centimetre pad.
- Dipping mattress you roll into: a new mattress.
Sources
Facts checked 23 October 2026
- Amazon listing (Degrees of Comfort) — Retailer listing, checked 23 October 2026
- Amazon listing (UsparkMC) — Retailer listing, checked 23 October 2026
- Amazon listing (Silentnight) — Retailer listing, checked 23 October 2026
- Silentnight — Airmax mattress topper product page — Manufacturer documentation, checked 23 October 2026
- Amazon listing (Silentnight) — Retailer listing, checked 23 October 2026
Can a topper fix a sagging mattress?
It can hide a shallow dip for a while. A two-layer foam topper with a firm base layer, such as the Degrees of Comfort 8 cm, bridges a dip you can feel but not see. A dip you roll into has lost the springs or the core foam underneath, and no topper restores that. Plan for a new mattress and use the topper to get there.
Is memory foam too hot?
Warmer than fibre, always. Gel infusions and mesh side panels, which the Uspark and Degrees of Comfort both list, take the edge off; they do not make foam breathe like hollowfibre. If you already wake up hot, choose fibre or the thinnest foam that solves your problem.
How long does a topper last?
Fibre flattens where you lie within a year or two, which is why Silentnight sells it with a two-year guarantee and a washable cover: you can fluff it, not restore it. Foam keeps its shape for longer but softens, and the cheaper foams soften faster. Neither outlives a decent mattress.
What size is a UK double?
135 by 190 centimetres, which is what every double topper on our shortlist is sold as. A UK king is 150 by 200, a super king 180 by 200, a single 90 by 190, a small double 120 by 190. A European double is 140 by 200 and needs an EU-size topper, not a UK one.
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