We use cookies to allow us and selected partners to improve your experience and our advertising. By continuing to browse you consent to our use of cookies. You can understand more and change your cookies preferences here.

Reviews based on facts
Our rigorous tests find the facts, and our impartial reviews tell you the truth about how products perform. First month £5, then £9.99 per month, cancel anytime.
Try Which?
16 February 2021

Cot mattress safety

Our tests have found multiple issues with cot mattresses. Find out how give your baby and toddler a safest sleeping space with our expert tips.
Cot mattress safety guide
Alison Potter

A crucial part of safe sleeping is choosing the best cot mattress. 

The Lullaby Trust, the UK's foremost organisation on baby safe sleeping, recommends that the safest place for your baby to sleep is on their own sleep surface, in the same room as you, for at least the first six months. 

Below are some of our top tips to choose the safest mattress for your child:

  • Make sure you choose the right size of cot mattress. The mattress should fit the cot with no gaps down the side that are more than 3cm.
  • Make sure the mattress is firm and flat, and protected by a waterproof cover (sometimes called a mattress protector).
  • Avoid second-hand mattresses where possible. Check any mattress you use conforms to current safety requirements.
  • Any mattress should carry the BSI number BS 1877-10:2011+A1:2012. It’s preferable if it also carries BS 7177:1996 and BS EN 16890:2017. See below for more information about these standards and what they mean.

Safety standards for cot mattresses

Cot mattresses that comply with the current British Standards give you confidence that what you’re buying for your baby is safe, and we would always encourage you to check whether your products are marked with a BS number.

With cot mattresses it’s slightly more complicated, as there are a number of BS numbers to look out for. BS 1877-10:2011+A1:2012 is an older mandatory standard that specifies the kinds of materials, construction and dimensions required when manufacturing mattresses, while BS 7177:1996 guarantees it has passed flammability standards.

There’s also a much newer cot mattress standard called BS EN 16890:2017, which was approved in September 2017. Although it’s currently a voluntary standard, it includes a number of requirements designed to test the performance and safety of cot mattresses.This includes:

  • Checking that no part of the mattress, for example the zip, can detach and become a choking hazard.
  • Checking the firmness of the top of the mattress, so if your baby accidentally rolls onto their front, their face won’t sink into the mattress and potentially suffocate them.
  • Checking whether the removable cover shrinks after washing, in case it compresses the mattress and causes a gap between the mattress and the bed frame where your child could trap a limb.

The BS EN 16890:2017 standard encompasses a wider set of tests and risks than the current mandatory standard and we feel it goes further with regards to child safety.

We test to this standard because we believe it goes further to ensure a safe sleeping environment for babies and young children.

Find out which mattress came out top in all these tests in our round- up of best cot mattresses.

Which cot mattress is best? 

We test the firmness, body support and durability of each cot mattress we review, so we can recommend the best to you.

If a mattress isn't firm enough to aid safe sleep and isn't sufficiently supportive then it becomes a Don't Buy cot mattress.

Our  Best Buy cot mattresses have passed all our robust safety tests.

Not a member? Join Which? to read our full cot mattress reviews.

New cot mattress for second baby? Buying second-hand?

Maybe you’re having baby number two and are thinking about using your first baby's cot mattress. Or maybe you’re considering buying and using a second-hand mattress.

When we surveyed 2,000 parents in February 2017 about cot mattresses, 12% of them told us they use a second-hand cot mattress, while 42% said they used the same cot mattress for more than one child.

But Which? tests have found that cot mattresses can lose more than 25% of their firmness in just a few years of use.

This means an older second-hand or hand-me-down mattress might not be firm enough for a newborn’s needs.

The Lullaby Trust recommends you buy a new cot mattress for your baby, where possible.

That's because it says there is some research that found an increased chance of sudden infant death syndrome (SIDS) when using a second-hand mattress, although the link is not yet proven.

If you have a second-hand mattress, whether it's a mattress you've used for one of your other children or one that’s been given to you, make sure:

  • The cot mattress is in good condition – it should be flat, firm, not soft or sagging, and should fit the cot without any gaps
  • It has been cleaned and dried thoroughly, and was previously used with a waterproof cover (and use it with a waterproof cover this time around)
  • It's free from cracks, tears or holes.

What is sudden infant death syndrome (SIDS)? 

Sudden Infant Death syndrome (or SIDS) is a term used to classify any sudden and unexpected death of a baby 12 months of age or younger. Sometimes referred to as 'cot death', it still isn't known for sure what causes SIDS, but there are steps that parents can take to reduce the risk of it happening. Parents are urged to follow safer sleep advice when putting their baby into his or her cot. This includes:

  • Keep your baby's cot in your room with you for the first six months. 
  • You should always place your baby on his or her back to sleep, not front or side (unless your doctor advises otherwise). If your baby rolls onto his or her tummy you should turn them onto their back again. Your baby should be put to down to sleep in this position until he or she is able to roll from back to front and back again.  
  • Place your baby with feet to the foot of the cot, so he or she can’t wriggle down under the covers. 
  • Don’t worry if he or she wriggles up and gets uncovered. 
  • It can be dangerous if your baby’s head gets covered when he or she sleeps. To avoid this, tuck in the bedclothes firmly around your child and no higher than his or her shoulders.
  • Never use a pillow, quilt or duvet if your baby is under one year old. Instead, use cotton sheets or lightweight blankets.
  • Alternatively, you can use a baby sleeping bag instead of bedding. 
  • The recommended room temperature for a baby to sleep in is 16-20ºC (61-68ºF) – use a room thermometer to check the temperature before putting your baby to bed.  
  • To check whether your baby is too hot, look for sweating or feel the back of your baby’s neck or his or her tummy, not hands or feet.

Overheating while sleeping and SIDS

It is very important that your baby does not overheat while sleeping as the chance of SIDS is higher in babies who get too hot while sleeping. 

Many cot mattress manufacturers make claims about their mattresses having extra features that provide a cooler sleeping surface for your baby, such as special construction or fabric.

It's important to know that your cot mattress won't single handedly be able to keep your baby from overheating, so make sure you follow the temperature advice above.

Also be careful of letting marketing claims on mattresses sway your buying decision. One of the things we test cot mattresses for is insulation and we classify each mattress in terms of the level of insulation it provides. 

Compare our cot mattress reviews to see the differences.

View all Cot mattresses