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Baby & child.

Updated: 2 Mar 2022

How we test cot mattresses

Our cot mattress reviews tell you how firm and supportive a mattress will be as your child grows, how easy it is to clean, and how resistant it is to leaks.
Sam Morris
Testing mattress 2

Babies sleep a lot. This means your cot mattress is going to be one of the most-used items you're buying for your newborn. 

Your baby will also grow quickly, which means a cot mattress needs to cope with the changing weight bearing down on it. And there are going to be plenty of little accidents coming its way as well. 

You want to make sure that your baby’s cot mattress will stand the test of time. We put all the mattresses we review through a variety of tests that simulate two to three years of use, meaning you can have the confidence that your cot mattress will hold up. 

Our cot mattress test is designed and informed by our years of testing experience. We buy all the mattresses we test ourselves, so you can be sure that the reviews you read are entirely independent and unbiased.

Our reviews seek to answer the key questions you'll want answered, such as: 

Find out which mattresses keep your baby supported in our cot mattress reviews.

Cot mattress safety standards

Our safety tests replicate those in the current cot mattress safety standard, which is called BS EN 16890:2017.

It was approved in September 2017 and it’s a voluntary standard, which means that it’s not a requirement. However, manufacturers are strongly encouraged to meet these standards to minimise risks and hazards for babies and young children.

The standard tests include checking for choking and swallowing hazards, such as loose zip pulls and stickers, as well as entrapment and suffocation risks.

In 2021 the standard was amended to BS EN 16890:2017 + A1:2021, and we updated our testing to be in line with the new version of the standard. 

Find out more about safety in our cot mattress and baby bedding safety guide

How well does the mattress support my baby?

We use a 12kg and a 21kg dummy to test how well the cot mattress is supporting your child as he or she grows. If the mattress is claimed to be reversible, we test using each dummy on each side of the mattress to give you a good idea of how good it is at providing the right support overall.

The dummies show us whether the cot mattress sags once weight is placed on it, or if keeps your child's body totally supported. 

A supportive mattress will help to keep your baby settled while sleeping.

Is the cot mattress firm enough?

Before we start any of our other tests, we test each cot mattress to see how firm it is. This means we can tell you how firm the mattress is when it's new, and how this compares with other mattresses. 

One of our tests investigates whether a mattress is firm enough to help prevent your baby from being smothered when they roll over on to their face while sleeping.

If the top layers of the mattress are too soft and your baby accidentally rolls on to their front, their face could sink into the mattress, which poses a suffocation risk.

It’s a concern with babies aged between four and 12 weeks, when they are typically able to roll over from their back to their front.

Rolling from front to back requires more strength, and in some cases a baby may not master this skill until they reach around six months old.

As well as sleeping on the cot mattress, your baby will also be bouncing on it and playing on it as he or she grows, and that's not to mention all the times you'll be sitting on it while reading bedtime stories. You want to make sure that through all this wear and tear, the mattress you choose is going to stay firm.

How durable is it?

Our tests put each cot mattress through the equivalent of roughly four to six years' use. This involves repeatedly hitting the mattress with a weight, to replicate your toddler jumping or sitting on it every day. We then record any changes to the mattress, including damage. 

A good mattress will be able to withstand our durability test and retain its firmness throughout. It should also not lose any of its height. This ensures that the mattress will remain safe and supportive for your child all the way up until they move on to a junior bed.

How resistant is the mattress to being penetrated by moisture?

The truth is that your cot mattress is going to be subjected to a lot of liquids. Babies get sick, their nappies leak, and numerous spills are inevitable.

Not only is it important that your baby doesn’t sleep on a damp cot mattress, but also that the mattress stays clean of any bad bacteria. But if liquids are settling deep into your baby’s cot mattress, it's going to be difficult to tell if it's still hygienic.

We test each cot mattress to see how resistant it is to moisture permeating its inner layers. We've found that some are very good at preventing this, while others allow liquids to pass through easily.

Does the mattress have good airflow?

We use special equipment to check the airflow through the mattress.

This is to assess how breathable it is, as it’s important for fresh air to circulate around your baby’s face.

It’s also to see whether the mattress draws away body warmth effectively so your baby doesn’t overheat.

How easy will it be to clean?

You will probably probably need to start cleaning your cot mattress from the get-go. 

If it comes with a removable cover, we'll check how easy this is to get on and off. You don’t want to be battling with an awkward cover when trying to clean a soiled mattress in the middle of the night.

We also assess how the mattress cover fares after several washes, and check to see if there is any shrinkage or bobbling to the fabric.

If a cover shrinks, then it could potentially compress the size of the mattress. The smaller dimensions might mean that the mattress no longer sits flush within the cot bed, and if there’s a gap of a few centimetres, there’s a risk that a baby can trap a limb and become stuck.

If your baby becomes trapped and is positioned face down, this could be a serious suffocation risk.

Should I buy it?

Each of the above tests counts toward a total test score. This score is the overall percentage you will spot next to each of our cot mattress reviews.

Not every aspect of the mattress has equal weight in the total test score. We've considered which aspects will be the most important, and have broken down the score as follows:

  • 50% performance (body support, height and firmness, resistance to moisture, and airflow)
  • 25% mechanical hazards (any entrapment risks, or suffocation and choking hazards)
  • 15% durability (loss of firmness and height over time)
  • 10% convenience (removing and cleaning the cover, cover shrinkage and re-fitting issues).

Our reviews completely ignore price.

A cot mattress that scores 70% or above gets a Best Buy recommendation, while one that scores 45% or below is a Don’t Buy – which means it's so poor that we recommend you avoid it.

A cot mattress is automatically downgraded to a 0% Don’t Buy if our tests highlight a serious safety risk.

Our cot mattress reviews are for Which? members, but any mattresses labelled 0% Don't Buys are given a safety alert that's free for anyone to read, as we believe it's our public duty to inform all parents about any serious hazards or risks that our tests have uncovered.