The answer to how thick should a mattress topper be depends on the change you want, the material selected and the condition of the mattress underneath. A deeper topper creates a more noticeable new comfort layer, but thickness does not tell you whether the surface will feel soft, firm, responsive or contouring.
The All Foam memory foam topper is available in 2.5cm, 5cm and 7cm options. The standard polyurethane and Reflex toppers are 5cm thick. These choices let you make a light adjustment, add a more substantial comfort layer or select the deepest memory foam option in the range.
Before choosing, check that the mattress remains level and supportive. A topper cannot repair sagging, broken springs or a failed support core.
The quick thickness comparison
A 2.5cm memory foam topper makes the lightest adjustment in the All Foam range. It adds a thin pressure responsive layer while allowing more of the existing mattress feel to remain noticeable.
A 5cm topper creates a clearer change. It is the middle memory foam depth and the fixed depth used for the medium density, high density and Reflex foam toppers.
A 7cm memory foam topper is the deepest option. It creates the most substantial memory foam layer and the strongest contouring change, but it also raises the bed by the greatest amount.
None of these depths is automatically best. The correct choice depends on the result you want.
What thickness changes
Thickness controls how much new material sits between the sleeper and the existing mattress. A thicker topper usually allows more of the topper's own character to be felt before the mattress underneath affects the surface.
With a thin topper, the original mattress remains a larger part of the overall feel. This can be useful when the mattress is broadly comfortable and only needs a light adjustment.
With a deeper topper, the material has more room to compress. This can make memory foam contouring more noticeable or make a firm foam layer feel more substantial.
Thickness does not change the condition of the support below. A 7cm topper over a dipped mattress still follows the dip.
What density changes
Density describes how much foam material is present within a given volume. It can influence durability and how a foam performs, but it is not the same as firmness.
A higher density foam is not automatically the hardest. A medium density and high density polyurethane topper can have different surface feels, while a memory foam topper responds differently again because it is a different material.
The foam density versus firmness guide explains why the two terms should not be used interchangeably.
When comparing toppers, consider material, density, firmness and thickness together. Choosing only by depth can lead to the wrong feel.
What firmness changes
Firmness describes resistance to compression and the general surface feel. The All Foam topper range includes softer, firmer and more responsive options.
The medium density foam topper provides a straightforward softer feel at 5cm. The high density foam topper gives a firmer, more stable 5cm layer.
The Reflex Superior Medium topper offers a resilient medium feel with quicker recovery than memory foam. The Reflex Superior Firm topper provides a firmer version of that responsive feel.
The memory foam topper responds more slowly to heat and pressure and follows the body more closely.
All five products can be compared at their actual listed thicknesses. The material tells you more about response than the number alone.
When 2.5cm may be suitable
Choose 2.5cm when the existing mattress is supportive and you want a light memory foam adjustment rather than a major change.
This depth can be useful when you still like the general firmness of the mattress but want a little more contouring at the surface. It also adds less overall bed height than the deeper options.
Because the layer is shallow, the mattress underneath remains clearly involved in the feel. A very firm mattress may still feel firm. A soft or uneven mattress will still feel soft or uneven.
Do not choose 2.5cm because it is cheaper if your real aim is a deep memory foam feel. Match the depth to the intended change.
When 5cm may be suitable
A 5cm topper is the most versatile depth in the range because it is available in several foam types.
Choose 5cm memory foam for a more noticeable contouring layer than 2.5cm without selecting the deepest option. Choose medium density foam when you want an immediate softer feel. Choose high density foam for a firmer and more stable surface.
Reflex Medium and Reflex Firm are also 5cm. They recover more quickly after pressure than memory foam and can suit customers who want a responsive surface rather than a slow contouring one.
The same thickness can therefore produce very different results. This is the clearest example of why material and firmness matter.
When 7cm may be suitable
The 7cm memory foam topper gives the deepest contouring layer in the All Foam topper range. It is most appropriate when you deliberately want a strong memory foam character and the existing mattress remains structurally sound.
A deeper topper increases total bed height and may require deeper fitted sheets. It can also change how easy it is to move on the surface because more slow response foam is involved.
Do not use the 7cm option as a way to hide a failed mattress. The deeper layer can make the bed feel different, but it cannot rebuild the support underneath.
Check the existing mattress first
Remove the bedding and inspect the mattress from above and from the side. Look for lasting hollows, collapsed edges, damaged seams and areas that compress much more easily than the rest.
Then check the bed base. A broken slat or bowed platform can create a dip that looks like mattress failure. Correct the base before deciding whether a topper is suitable.
A topper is most appropriate when the mattress is level and supportive but the surface feel needs changing. The mattress topper or new mattress guide gives a full condition checklist.
Consider sleeping position and body weight
A side sleeper may want more cushioning around the shoulder and hip, while a front sleeper may prefer less sink through the centre of the body. Back sleepers often look for an even and stable surface.
These are general comfort patterns, not rules. Body weight changes how deeply the topper compresses. A lighter person may engage less of the material, while a heavier person may feel more of the mattress underneath.
The same 5cm topper can therefore feel different to two people. Use your current mattress as a reference and describe the change you want.
Check total bed height
Add the topper depth to the existing mattress depth. A 7cm topper on a deep mattress can create a much higher sleeping surface.
Check whether the bed remains easy to get into and out of. Consider headboard height, bedside furniture and any guard rail on a raised bed. Confirm that fitted sheets and protectors can cover the combined depth.
A topper that overhangs or is forced into tight bedding may move or curl. Measure the sleeping surface and check the listed dimensions before ordering.
Standard All Foam topper sizes
All Foam toppers are available in:
- Single: 90cm by 190cm.
- Double: 135cm by 190cm.
- King Size: 150cm by 198cm.
- Super King: 180cm by 198cm.
Measure the mattress itself, not only the bed frame label. Older and imported mattresses may differ from the size you expect.
For a non standard or shaped topper, contact All Foam before ordering. The custom cut topper sizing guide explains the information required.
Toppers for guest beds, airbeds and sofa beds
The memory foam topper can be used on suitable guest beds, airbeds and sofa beds. Check that the surface is even and can support the topper properly.
Consider storage. Foam should not remain tightly folded or compressed for long periods. A thick topper also requires more storage space and may prevent a sofa bed from closing.
Measure the unfolded sleeping area and confirm that the selected depth will not interfere with hinges, frames or bedding. Follow the furniture manufacturer's instructions.
Heat and response
Memory foam responds to warmth and pressure, so its feel can change as it warms during use. A deeper memory foam layer may create a more enveloping feel.
Reflex and standard polyurethane foams recover more quickly. This does not guarantee that one material will sleep cooler or suit every person. Room temperature, bedding, protector, body heat and ventilation all contribute.
Choose according to response and comfort preference rather than a simple cool or warm label.
Common thickness mistakes
Choosing the thickest topper because it appears more luxurious is one mistake. More material creates a bigger change, which may be the opposite of what you need.
Choosing by thickness while ignoring foam type is another. A 5cm memory foam topper and 5cm high density topper do not feel the same.
Using a topper over a sagging mattress is a third. The new layer follows the old shape.
Ignoring bed height and sheet depth can also create practical problems. Measure the complete setup before ordering.
Finally, do not expect a topper to diagnose or treat pain. It changes surface comfort. Persistent pain needs appropriate professional advice.
A simple selection process
First, inspect the mattress and base. Second, decide whether you want a lighter or more substantial change. Third, choose the response, either slow contouring memory foam, immediate polyurethane foam or responsive Reflex foam. Fourth, check the total bed height and exact size. Fifth, review the returns and care information.
A practical starting point is:
- 2.5cm memory foam for a light contouring adjustment.
- 5cm for a noticeable change with the widest material choice.
- 7cm memory foam for the deepest contouring layer.
This is guidance, not a guarantee of feel.
Final answer
A mattress topper should be thick enough to create the change you want without hiding a structural problem or making the bed impractically high.
Choose 2.5cm for a lighter memory foam adjustment. Choose 5cm for a more noticeable layer and the widest choice of foam types. Choose 7cm when you deliberately want the deepest memory foam response.
Then compare density, firmness and material. Check the existing mattress, measure the bed and contact the All Foam team when the required size or feel is uncertain.