Can you put a mattress on top of another mattress?
Sleeping on a stack of mattresses may sound like comfort heaven, but it's not great news for your back. We explain why
Putting one mattress on top of another (and maybe another, and another) is not just the stuff of fairytales. Mattress stacking is a space-saving way to store an extra mattress, and can even create an irresistibly soft, lofty and bouncy sleeping surface.
But just because you can put one mattress on top of another, doesn’t mean you should. All the best mattresses we’ve reviewed here at Expert Reviews are designed to deliver consistent comfort and support every night for a decade, but only when they’re positioned on a suitable bed base – not on top of another mattress.
In this article, we’ll explore the many reasons why putting a mattress on top of another mattress is bad for both you and the mattress: from wasted warranties to musculoskeletal misery.
Why might I want to put one mattress on top of another?
Sleeping on a stack of two or more mattresses is something many of us have done at one time or another. A few of these reasons may be familiar to you:
- If you’ve just taken delivery of a new mattress and aren’t sure what to do with the old one yet, it may make sense to stack the new one on top until you’ve figured it out.
- If you’re short on space but want to keep a spare mattress around for occasional visitors, where better to store it than immediately under your own mattress? Saves money on a bedstead, too.
- If you have two thin, firm mattresses, you may find them more comfortable doubled up. After all, the best hybrid mattresses comprise a number of layers, so you might think stacking two or more thin mattresses follows a similar principle.
- If you like a soft, bouncy sleeping surface, you may discover that a stack of mattresses is your ultimate sleep cocoon.
All of these strategies will do little harm in the short term, but it’s not a good idea to allow them to become a habit. At best, your bed will be more difficult to make in the morning; at worst, you’ll end up with back pain issues.
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Why shouldn’t I put one mattress on top of another mattress?
Stacking mattresses can damage your sleep, your back and your bed. Let’s break down the reasons for each of these decidedly undesirable outcomes.
Mattress stacking makes the surface too soft
To an extent, mattress firmness is a personal preference. One hybrid mattress we’ve reviewed – the Eve Wunderflip Premium Hybrid – offers a softer side and a firmer side so you can choose which suits you best.
However, if a mattress doesn’t offer enough support to allow your spine to align, it’s objectively too soft for you. Over time, an unsupportive mattress will put pressure on your spine and cause long-term back pain.
This may happen if you spend too long sleeping on a stack of mattresses. All mattresses are designed to be placed on a bed base, either solid or slatted. If they’re placed on top of another mattress, they won’t offer the support they’re designed to.
I tested this with a couple of mattresses I’m currently reviewing. On a solid bed base, the central sleeping surface of the Emma NextGen Premium sank 24mm under 7.5kg of weights, which is fairly standard for a high quality hybrid mattress. Stacked on top of another Emma mattress, it sank 32mm under 7.5kg. Stacked on top of two mattresses, it sank 42mm under 7.5kg.
If you translate that 7.5kg test weight into a 75kg human being, it suggests a significant increase in sinkage on a mattress stack compared with a solid bed base.
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Mattress stacking creates uneven support
Many mattresses sink slightly more at their edges than in their middle, especially when they’ve been used for a while. This effect is exaggerated when you put one mattress on top of another. Sit on the edge of the bed, and it may struggle to support your weight.
Again, I put this to the test. Under 7.5kg of weights, my Emma NextGen Premium sank 27mm at the edge when on a bed base. When on top of another mattress, it sank 38mm.
Certain types of mattress perform especially poorly when stacked on top of other mattresses. A foam mattress needs a strong, solid base to deliver consistent support, and if you use a lumpy old mattress under it the foam mattress will amplify all the lumps and bumps.
If you stack two sprung mattresses on top of each other, you’ll double down on their bounciness. As fun as this may sound, it will not make for peaceful sleep. It will also exaggerate any movement your partner makes in the night.
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The mattresses can move around
Many conventional mattresses have a silky surface, which can make it easier to flip them and sleep on either side (albeit with a sheet). Imagine that silky surface trying to stay in place on top of another silky surface while you and your partner toss and turn in the night. Unless you’ve strapped the mattresses together, they won’t stay in place, and neither will you.
Most of the mattresses we review here at Expert Reviews are hybrids and bed-in-a-box mattresses that have a non-slip base, but these bases are designed to be non-slip on a bed base, not on top of another mattress.
The mattresses may get damaged
When your stack of mattresses shift and wobble in the night, the best that can happen is you’ll have to wrestle the whole thing back together in the morning. The worst is that both mattresses will suffer damage to their surfaces and structure, with springs being warped and eventually failing.
Damage is more likely to occur to the mattress at the bottom of the stack, because it will have to support more weight than it’s designed to. A king size Simba Hybrid Pro weighs 49kg, so if you put one of these mattresses on top of another it will take you almost half-way to Simba’s per-person weight limit of 114kg before you even get in bed.
You may void your mattress warranty
Mattress warranties usually require the product to be used as the manufacturer intended, and this does not include stacking.
For example, Emma’s 10-year guarantee covers your mattress against “sags or dips that occur within your mattress despite correct usage” and explicitly excludes “any condition resulting from misuse or abuse of the product” such as “improper ventilation”, which would include stacking.
Simba goes further and states that its 10-year warranty will not be honoured if you don’t use a “suitable bed base”. It specifies that slats should be more than 2in wide and no more than 3in apart, and does not recommend surfaces that “prevent the mattress from breathing and ventilating”.
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Multiple mattresses make you too hot
Experts recommend that the healthiest and most comfortable sleep conditions include a temperature of 16 to 18°C and relative humidity of 30 to 50%.
The best mattresses we review – such as the Simba Hybrid Pro and the Otty Pure Hybrid Bamboo & Charcoal mattress – do a good job of temperature regulation to keep you cool, prevent clammy and uncomfortable nights.
However, this temperature regulation won’t be as effective when the mattress is placed directly on top of another mattress. Piling mattresses together traps air and heat, pushing temperature and humidity too high for comfortable sleep.
To put this to the test, I used a hot heat pad and thermometer to measure how two new mattresses, the Emma NextGen Premium stacked on the Simba Hybrid Pro, retained heat.
As expected, the mattresses held onto more heat when stacked. A covered heat pad took 10 minutes to fall from 50°C to 26.1°C when the mattress was on a slatted bed base. When stacked on top of another mattress, it took 15 minutes to cool to the same level.
I carried out this test on a balmy July evening when the ambient temperature was 22°C, but I was still surprised by how much longer the stacked mattress held onto the warmth from the heat pad.
Mattress stacking encourages mites and mould
Stacking mattresses prevents air from flowing in and around each mattress. As well as retaining heat, this encourages unwanted guests that thrive in warm, airless conditions: bacteria, allergens, mould and dust mites.
Studies estimate that one mattress houses between 100,000 and 10 million microscopic dust mites. These beasties thrive in temperatures of 20 to 25°C and humidity levels of 70 to 80%, so doubling up your mattress more than doubles up your mite count, because it enhances the environment they love.
The problem gets worse if your mattress stack lasts long enough for mould and mildew to form in between the surfaces. These fungal organisms thrive in damp conditions and multiply fast, sending out spores that can trigger allergies and irritate your breathing, which in turn disrupts your sleep. At worst, they can seriously damage your lung health.
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How can I make my mattress higher and softer without stacking?
If the main reason for your mattress stacking was the pursuit of softness and height, then a mattress topper may be all you need, and you can buy one for as little as £30.
A mattress topper is effectively a slim mattress, designed to sit on top of your existing mattress rather than be used on its own. Our roundup of the best mattress toppers includes plenty of options that work as a layer of softness on a mattress that’s too firm.
The best mattress toppers may help you solve your mattress storage problems, too. Instead of storing a spare mattress under your current one, buy a relatively thick mattress topper that you can roll up in the wardrobe or store under your bed (not under your mattress).
Mattress toppers aren’t designed to be used on their own every night, but a casual overnight visitor would find a topper more comfortable than the sofa – and it will be much easier for you to store than a whole spare mattress.
