Cot mattress and baby bedding safety

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

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. 

While there are countless pieces of baby bedding available to buy, you don't need that much to keep your baby comfortable and safe while sleeping. 

Read on for our expert advice on getting the safest cot mattress and bedding for your little one.

Top cot mattress safety tips

1. Make sure you choose the right size of cot mattress for your cot. The mattress should fit the cot snugly, with no gaps between the side of the mattress and the cot frame.
2. Make sure the cot mattress is firm, flat and protected by a waterproof cover.
3. Avoid second-hand cot mattresses where possible. If you need to, look at our checklist to make sure it is safe to use.
4. Look out for safety standards. All mattresses should have the BS 1877-10:2011+A1:2012 number on the labelling or instructions. It's preferable if it also carries BS 7177:1996 and BS EN 16890:2017 + A1:2021.

Still looking for a cot bed? Read our guide on how to buy the best cot bed. 

Cot mattresses safety standards

Cot mattresses that comply with the current British Standards (BS) 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. 

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 voluntary cot mattress standard called BS EN 16890:2017 +A1:2021, which was approved in September 2017. Although it’s currently voluntary, it encompasses a wider set of tests and risks than the current mandatory standard, designed to test the performance and safety of cot mattresses:

• 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 on to their front, their face won’t sink into the mattress and potentially suffocate
• 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.

We test to this standard because we believe it goes further to ensure a safe sleeping environment for babies and young children. Some cot mattresses we've tested, which claim they conform to the voluntary standard, fail key safety tests. So our cot mattress reviews really do reveal the safest and best cot mattresses on the market. 

Find out which mattress came out top in our tests in our round-up of the Best Buy cot mattresses.

Should you buy a second-hand cot mattress?

We do not recommend buying or using a second-hand cot mattress. Where possible, always buy new. This is also the advice of The Lullaby Trust.

Which? tests have found that cot mattresses can lose more than 25% of their firmness in just a few years of use. This means using a second-hand or hand-me-down cot mattress may not provide the firm support all babies need, which could increase the risk of suffocation or smothering.

The Lullaby Trust also 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.

When we surveyed 1,878 parents in February 2021 about cot mattresses, almost two in five told us they use a second-hand cot mattress.

Cot mattress ownership:

• new (61%)
• second-hand – given to them (23%)
• second-hand – purchased (16%)

Out of all the second-hand cot mattresses purchased, nine in 10 came from Facebook Marketplace, Amazon Marketplace or eBay.

Buying from an online marketplace carries some risk as you can't be certain of the history and quality of a second-hand cot mattress, meaning there is a greater chance of it having problems.

This is backed up by our survey: around half of parents with a new cot mattress said they had issues with it, but this increases to around nine in 10 parents facing problems when the cot mattress was second-hand.

In fact, all types of issues identified in the survey are significantly more common in second-hand cot mattresses.

Most concerning is that a quarter of second-hand cot mattress owners reported indentations forming in the mattress or it sagging too much. A mattress that isn't firm and flat won't provide enough support for your baby, and it could pose a suffocation risk.

Buying new doesn't have to break the bank. We compared the prices of cot mattresses that we've tested and found the average price of a Best Buy is £96, while the average price of a Don't Buy is £135!*

If you have to buy second-hand, it's worth seeing whether you can check the cot mattress yourself before parting with your money. If a reseller won't let you find out more about the history of a second-hand cot mattress, we'd advise looking elsewhere.

 Use our checklist below to make sure a second-hand cot mattress is going to be fit for use:

1. Make sure the cot mattress was previously protected by a waterproof cover This will reduce the risk of unhealthy bacteria lurking in the mattress.
2. Test whether it's still firm and lies flat, with no holes or tears When you press down there should be resistance and the mattress should spring back immediately after you remove your hand.
3. Check the mattress isn't sagging in places Otherwise, that part of the cot mattress won't provide enough support for your child, and if a baby ended up face down in the sagging area it could be a suffocation risk.
4. Make sure it fits the cot bed with no gaps around the edges Take a tape measure and check the length and width of the mattress at multiple places on the mattress. The standard size mattress for a UK cot bed is 140cm x 70cm, but double-check the cot mattress size needed for your cot bed beforehand.
5. Clean the waterproof layer and air-dry thoroughly before reusing the mattress To make sure it's dirt and bacteria-free before your little one uses it.

Find a safe new cot mattress with our how to buy the best cot mattress guide

What is sudden infant death syndrome (SIDS)? 

Sudden infant death syndrome (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 parents can take to reduce the risk of it happening.

Overheating while sleeping and SIDS

It's very important 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.

Also be wary 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.

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 our safe sleeping advice below.

Compare our cot mattress reviews to see the differences.

10 baby safe sleeping tips

Baby charity the Lullaby Trust advises parents to follow these cot and sleep-safety tips:

1. Keep your baby's cot in your room with you for the first six months. 
2. Make sure the mattress is firm, dry and clean.
3. The safest sleeping position for your baby in a cot is lying on their back, not on their front or side (unless your doctor advises otherwise), until your baby is able to roll from back to front and back again.
4. Place your baby with their feet to the foot of the cot, so they can’t wriggle down under the covers. Don’t worry if they wriggle up and get uncovered. Alternatively, you can use a baby sleeping bag instead of bedding.
5. It can be dangerous if your baby’s head gets covered when they're sleeping. To avoid this, tuck in the bedclothes firmly around your child, and no higher than shoulder level.
6. Never use a pillow, quilt or duvet if your baby is under a year old. Instead, use cotton sheets or lightweight blankets.
7. The recommended room temperature for a baby to sleep in is 16-20ºC (61-68ºF) – use a room thermometer to check before putting your baby to bed. 
8. 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.
9. Keep the cot out of direct sunlight.
10. Babies need to lose excess heat from their heads. So if you've been out with your baby and they fall asleep, remove their hat and extra clothing as soon as you come indoors or enter a warm bus, train or shop, even if it means waking your baby.

Best cot bed brands – see how parents rate the top cot bed brands, from Mamas & Papas, Ikea and John Lewis

Baby bedding essentials

Before your baby arrives, it makes sense to stock up on some basic baby bedding. Go for a minimum of:

• three bottom sheets
• three top sheets
• three blankets.

You'll more than likely get blankets as presents, but it's always useful to have a few extra. 

Baby sheets

Fitted sheets

These are very useful, especially as your baby gets older and moves around in the cot more. A fitted sheet won’t ruffle and come away from the mattress as a result of a squirming baby. However, they can be tricky to fit if the cot mattress you've bought is quite stiff and heavy.

Fitted sheets tend to be made of cotton jersey or terry (fine towelling cotton/polyester mix), which won't require ironing.

Flat sheets

These tend to be used as a top sheet in combination with a blanket. They're fine for use as a bottom sheet too, but are generally more awkward to put on than fitted sheets.

Flat sheets tend to be made either from flannelette or plain cotton. Plain cotton has the advantage that it can be washed at higher temperatures, although it doesn’t feel as soft as flannelette.

Baby blankets

The types of blankets most commonly available are cotton cellular, acrylic cellular and fleece.

Cotton cellular blankets

The cellular structure of these 100% cotton blankets means they're warm in winter and cool in summer. They're also lightweight and are washable at higher temperatures than fleece or acrylic.

Acrylic cellular blankets

These are extra-lightweight and quick drying, with the same year-round usefulness as the cotton cellular type. They're similar in price to cotton cellular blankets but tend not to be as soft on the skin as cotton or fleece.

Fleece blankets

These are made from 100% polyester, are soft for your baby and easy to wash and dry. They tend to be more expensive than other types, though.

Baby coverlets and comforters

A coverlet or comforter is a lightweight baby bedding version of a quilt that can safely be used for babies under one year old, because it doesn't have the soft padding of a standard quilt. It's as warm as a sheet and blanket combined.

Always follow the manufacturer's instructions before using a coverlet, as some aren't suitable for babies under 3.5kg or 7lb 12oz.

Baby sheepskin fleeces

These are basically mini sheepskin rugs. They're designed to be soft and comforting for babies to lie on, and many parents feel they calm and soothe newborns. If you buy one, make sure it's specifically for baby use.

Keep your little one safe: discover our expert advice on using cot beds safely

Quilts, duvets and pillows safety advice

Quilts, duvets and pillows shouldn't be used for babies under one year old. 

After this, it's fine to replace baby blankets and top sheets with a cot quilt or duvet if you wish. For toddlers, we recommend starting off with a light 3-4.5 tog before moving up to a higher tog as they grow. Make sure they still have access to a blanket, so they can regulate their own temperature if needed. 

Avoid using a 10.5 tog or higher until your child is aged 10.

Pillows can also be safely used from the age of one year, but don’t feel you have to buy one. Your baby will be used to sleeping without one and may even not want it in the cot.

Video: baby sleeping bag safety

In July 2020 we tested 15 baby sleeping bags from a range of well-known brands and online marketplaces. Our tests uncovered serious issues with seven of the sleeping bags. Find out more in our baby sleeping bags investigation. 

Watch our video below to learn about four products you should steer clear of. They're listed as baby sleeping bags by the sellers on online marketplaces, but they're not the traditional-style sleeping bags and we'd advise against buying them.

According to The Lullaby Trust, sleeping bags should be cotton, lightweight and not have a hood. Make sure the sleeping bag is not too big around the neck, to prevent your baby from slipping down into the bag.

Sleeping bags designed for babies and young children usually have a full-length front zip or poppers at the shoulders, and sometimes a zip at the side with sleeveless arm holes. Rather than tucking your baby up at night under sheets and blankets, you simply zip or popper them into the bag.

Cot bumpers

These are soft pads that are tied to the sides of the cot, designed to give babies some protection from the hard sides. We don't recommend you get them. According to The Lullaby Trust they can pose the risk of an accident to your baby once they begin to roll and move about the cot. 

There have been a number of cases in the UK and abroad where infants have become entangled in the ties and material, or fallen from pulling themselves up on the bumpers.

Baby sleep positioners, pods and nests

Baby sleep positioners, cushioned sleeping pods and baby nests are popular with parents, but we have concerns.

In October 2017, several prominent retailers (including eBay, John Lewis and Tesco) stopped selling these products for babies under six months, citing concerns over safety. 

These products do not provide a flat, safe sleeping surface and they pose a risk of suffocation if your baby rolls on to their front. So they should never be used without supervision. 

There have been 13 infant deaths in the US between 1997 and 2011 linked to the use of sleep positioners. The Food and Drug Administration (FDA) in the US released a statement warning about these items, which are also known as 'anti-roll' products, warning parents not to buy or use them.

Which? doesn't review these products, and current safe-sleeping advice from The Lullaby Trust is to keep cots clear of pillows, toys, bumpers and sleep positioners, because the evidence shows that this reduces the risk of sudden infant death syndrome (SIDS).

*Price of cot mattresses tested by Which? as of May 2021