Memory Foam Topper Made to Measure: Thickness, Density & Sizing Guide
A memory foam topper is a separate layer of slow recovery foam that sits on top of a mattress to make it softer and spread your weight more evenly. Most people choose a 5cm (2 inch) topper, which adds a noticeable comfort layer without making the bed feel unstable. GB Foam Direct cuts memory foam toppers to any size and shape, so the same topper works on a standard bed, a caravan island bed or a campervan rock and roll bed, and we also sell a ready-made topper in standard bed sizes.
Key takeaways
- A 5cm (2 inch) topper suits most beds. Choose 2.5cm (1 inch) for a light softening layer and 7.5cm (3 inches) or more for a deep, cushioned feel.
- Our GB 55M memory foam has a density of 47.5 to 52.5 kg/m3 (BS EN ISO 845) and a nominal hardness of 47 to 63 N (BS EN ISO 2439).
- A topper improves comfort on a firm or uneven surface, but it will not fix a mattress that has sagged. Replace the mattress if it dips.
- Measure the top surface of the mattress, not the bed frame, and use a template for shaped caravan, campervan and boat beds.
- Our memory foam carries a 5 year guarantee against faults in manufacture, and orders placed before 11am Monday to Thursday are eligible for next working day delivery.
What Is a Memory Foam Topper?
A memory foam topper is a removable layer of viscoelastic foam placed on top of an existing mattress. Most are 2.5cm to 7.5cm (1 to 3 inches) thick, and we cut deeper toppers to order. Our memory foam reacts to body heat and pressure, so it moulds around your shoulders and hips and then returns slowly to its original shape when you get up.
That slow recovery is what separates it from the high density polyurethane foam used in sofa seats, which springs back straight away. Because memory foam is soft and slow to respond, it works best as a comfort layer on top of a firmer support layer, rather than on its own.
We use the same principle in our own memory foam mattresses, which typically put 5cm of memory foam on top of a 16cm support layer.
What Thickness of Memory Foam Topper Do You Need?
The right thickness depends on how firm your mattress is now and how much softness you want to add. Thicker toppers feel softer and more enveloping, while thinner toppers change the feel of the bed less.
| Topper Thickness | Feel | Best For |
|---|---|---|
| 2.5cm (1 inch) | Light softening layer | A comfortable mattress that needs only a little extra softness, guest beds and sofa beds that are folded away |
| 5cm (2 inches) | Noticeable comfort with stable support | Most double and king size beds, caravan and campervan beds, firm mattresses |
| 7.5cm (3 inches) | Deep, cushioned feel | Very firm mattresses and side sleepers who want more give at the shoulder and hip |
| 10cm (4 inches) and deeper | Very soft, deep comfort layer | Turning a thin or firm base into a soft bed, such as a seat-bed made from cushions |
A thicker topper also raises the height of the bed, so check that fitted sheets and any bed rails or caravan locker lids still clear it before you order 7.5cm or more.
What Density Should a Memory Foam Topper Be?
Density decides how long a memory foam topper keeps its shape, and hardness decides how soft it feels. Density is the weight of foam per cubic metre, measured in kg/m3, while hardness is measured in newtons (N). A higher density memory foam resists body impressions for longer.
These are the figures for the memory foam we cut, taken from its technical datasheet, alongside two of our high density upholstery grades for comparison.
| Foam | Density (kg/m3) | Hardness (N) | How It Behaves |
|---|---|---|---|
| GB 55M Memory Foam | 47.5 to 52.5 | 47 to 63 | Slow recovery, moulds to the body, best as a topper or comfort layer |
| GB 39S Luxury Soft | 37 to 41 | 100 to 140 | Soft and springy, recovers instantly, with none of the slow sinking feel of memory foam |
| GB 39H Luxury Hard | 37 to 41 | 180 to 220 | Firm and supportive, used as a support layer under memory foam |
The comparison shows why memory foam feels so different. It is denser than our luxury upholstery grades but far softer, so it gives a sinking, pressure relieving feel, while its higher density helps it hold its shape over long-term use. For more on how density and hardness differ, see our guide to high density foam.
Which Memory Foam Topper Should You Choose?
| Situation | Recommended Option | Why |
|---|---|---|
| Mattress feels too firm | 5cm GB 55M topper | Adds a soft comfort layer while the mattress underneath still provides support |
| Standard single, double, king or super king bed | Our ready-made memory foam mattress topper | 2 inches of 50kg/m3 memory foam with a zipped, machine washable cover, made in the four standard UK bed sizes |
| Mattress has dips or sagging | Replace the mattress | A topper follows the shape underneath it, so it will sink into the same dip |
| Caravan or campervan bed made from seat cushions | 5cm to 7.5cm topper cut as one piece | One continuous layer bridges the joins between cushions for a smoother sleeping surface |
| Shaped bed, such as an island bed with rounded corners or a boat berth | Custom shape topper cut from a template | Our cutters follow your template so the topper fits the mattress edge exactly |
| Guest bed or sofa bed | 2.5cm to 5cm topper | Improves comfort on an occasional-use bed and is light enough to roll and store |
Our ready-made memory foam mattress topper comes in single (90cm x 190cm), double (135cm x 190cm), king (150cm x 200cm) and super king (180cm x 200cm), so you can order it without measuring if your mattress is a standard size. Choose a cut to size topper for any other size, shape or thickness. If your bed was bought abroad or you are not sure which size you have, our guides to single bed sizes, double bed sizes and king size bed sizes compare UK mattress dimensions with those used in Europe, North America and elsewhere.
If you want a complete mattress rather than a topper, you can ask for memory foam to be laminated to a firmer support foam when you order.
How to Measure and Order a Made to Measure Memory Foam Topper
Measuring the mattress itself, rather than the bed frame or the old topper, is the single biggest factor in getting a good fit. Follow these steps.
Measure the top of the mattress. Measure the width and length across the sleeping surface, edge to edge, in centimetres or inches. Do not measure the bed frame or base, which is usually larger.
Record any shaped corners or cut-outs. For rounded corners, angled ends or cut-outs around a door or locker, draw round the mattress on paper to make a template. Use the mattress or its cover as the guide, not old foam that may have shrunk or deformed.
Choose your thickness. Use the thickness table above. A 5cm (2 inch) topper suits most beds, and you should check the extra height still clears sheets, rails and locker lids.
Pick a shape and enter your size. Choose a standard shape on our foam cut to size page and enter your measurements, or select the custom shape option and send us your template.
Select memory foam. Choose our GB 55M memory foam as the foam type. If you want a full mattress, request a firmer support layer laminated underneath.
Let the topper recover before use if necessary. Memory foam usually returns to full size within 3 hours but can take up to 24 hours, and any new foam smell fades as it airs.
Benefits of a Memory Foam Topper
- Pressure relief. Memory foam moulds around prominent areas such as the shoulders and hips, spreading your weight over a larger area.
- A cheaper change than a new mattress. If your mattress is still supportive but too firm, a topper changes how it feels at a fraction of the cost of replacing it.
- Smoother sleeping surface. On caravan, campervan and boat beds made from several cushions, a single topper covers the joins.
- Hypoallergenic. Our memory foam is naturally hypoallergenic and antibacterial.
- Exact fit. Cut to size, a topper sits flush with the mattress edge instead of overhanging or leaving gaps.
Why Buy a Memory Foam Topper from GB Foam Direct?
GB Foam has been converting foam in High Wycombe since 1976, and we cut every topper to the measurements or template you send. Our factory combines CNC cutting with experienced freehand foam cutters, we work to ISO 9001 quality standards, and our memory foam carries a 5 year guarantee against faults in manufacture. For vehicle beds, our caravan mattress guide and campervan mattress guide cover the layouts we cut most often.
Speak to Our Team
If you need help choosing a topper thickness or making a template, call us on 01494 441177, email sales@gbfoam.com or fill out our contact form. We are in the office from 9am to 5pm Monday to Thursday and 9am to 3pm on Friday.
Memory Foam Topper FAQs
What thickness of memory foam topper is best?
A 5cm (2 inch) memory foam topper is the best choice for most beds. It adds a noticeable comfort layer without making the bed feel unstable. Choose 2.5cm (1 inch) for a light softening layer, or 7.5cm (3 inches) and above if your mattress is very firm or you sleep on your side.
What density should a memory foam topper be?
A good memory foam topper should have a density of around 50 kg/m3. Our GB 55M memory foam has a density of 47.5 to 52.5 kg/m3, tested to BS EN ISO 845, which helps it resist body impressions over time. Density affects how long the topper lasts, while hardness, measured in newtons, affects how soft it feels.
Can a memory foam topper fix a sagging mattress?
No. A memory foam topper follows the shape of the surface underneath it, so it will sink into any dip in the mattress. A topper is the right choice when a mattress is still supportive but feels too firm. If the mattress sags, replace it.
How long does a memory foam topper take to expand?
A memory foam topper usually expands to full size within 3 hours of unpacking, but it can take up to 24 hours. Unpack it in a warm, well ventilated room and leave it flat until it has fully recovered.
Does a new memory foam topper smell?
New memory foam can have a mild smell when it is first unpacked. Leaving the topper to air in a well ventilated space allows the smell to fade. This is normal for new foam and is not a sign of a fault.
Can I get a memory foam topper cut to size for a caravan or campervan?
Yes. GB Foam Direct cuts memory foam toppers to any size or shape, including island beds with rounded corners, rock and roll beds and boat berths. Choose a standard shape and enter your measurements, or select the custom shape option and send a paper or digital template.
What is the difference between a memory foam topper and a memory foam mattress?
A memory foam topper is a thin comfort layer placed on top of an existing mattress. A memory foam mattress combines a memory foam comfort layer with a firmer support foam underneath, such as 5cm of memory foam on a 16cm support layer. If your current mattress no longer supports you, a full mattress is the better choice.
How do I clean a memory foam topper?
Use a removable, washable cover and wash the cover rather than the foam. Our ready-made memory foam mattress topper comes with a zipped, machine washable cover. For marks on the foam itself, spot clean gently with a damp cloth and mild detergent, then let it dry completely before use. Our guide on how to clean foam covers this in more detail.
Cameron has emerged as a key marketing expert since joining GB Foam Ltd in 2017. A graduate of the University of Winchester, with a professional background in Public Relations; he has combined his content writing and brand awareness expertise with an in-depth knowledge of foam products and foam conversion technology to enhance the company’s marketing strategies and industry presence. Cameron has led numerous marketing campaigns, in both B2B and B2C segments, to further brand recognition and open up new business avenues worldwide.