What makes a cot mattress safe?

Posted by Megan Petschel & Julie Monson on

Choosing a safe cot mattress

Choosing a mattress for your baby’s cot is an important aspect of ensuring they sleep safely. With so many options on the market providing different benefits, it is important to know what to look for and that you are making the safest choice for your baby. So, what makes a cot mattress safe? 

A safe mattress is one that is firm and fits your baby’s cot snuggly so that there is no more than a 2cm gap between the mattress and the cot. The mattress should lie flat in the cot and no bulges should be visible. The condition of the mattress also has a direct impact on how safe it is to use. This means that there should be no indentations, sagging around the edges and holes, cracks or tears in the mattress. Adjustments such as placing sheepskin or a pillow on top of the mattress as well as using pillows to elevate part of the mattress must be avoided. 

Whilst making sure that the mattress you select is firm and fits the cot correctly, there are still other areas to explore to help create a safe sleeping environment for your baby. 


There is no one mattress that we are aware of that stands above the rest in terms of safety. Though, there are mattresses that meet the required standards from testing and those that do not. However, there are a few things which can make the mattress safer and should be considered:

Firmness of the mattress:

A mattress which is too soft increases the risk of SIDS and suffocation.   

  • This can happen if your baby were to roll onto their tummy and their face rested on the mattress. The mattress could potentially make it difficult for them to breath if their mouth and/or nose was covered by the mattress.       
  • When assessing the firmness of the mattress, it is advised that you press the middle as well as the edges with a firm flat hand.      
  • A mattress which bounces back immediately after being pressed indicates that it is firm enough for your baby to sleep on.      
  • It should also not be too easy to make an indentation in the mattress when you press it. Memory foam mattresses are therefore not recommended. A more scientific test using CDs and 2 litres bottles can be carried out to ensure the mattress your baby sleeps on is firm enough.

    Follow the link for step-by-step instructions.

Size of the mattress:

  • It is crucial that the size of the mattress fits the size of the cot that your baby will sleep in.      
  • A gap of 2cm or more between the mattress and side of the cot can result in your baby’s limb or head accidentally getting stuck which can restrict their airway and lead to suffocation.      
  • A mattress that is too big for a cot will likely bulge in the middle. This too increases the chances of suffocation.

How to test firmness of a cot mattress


According to British safety specifications, a mattress should not be thinner than 8cm. This is because your baby’s weight will be focused in one area of the mattress and a mattress which is too thin will not be able to support them adequately. It is also advised that the mattress does not exceed 15cm as to ensure that your baby is not able to climb out of their cot when they get bigger. 


Unfortunately, mattress sizes in South Africa are not straight forward. Internationally there are two regulated cot sizes which makes buying a mattress simple. A standard cot measuring around 120 x 60 x 15cm and a large cot measuring around 140 x 83 x 95 cm. 

Whilst South Africa has cots that are those sizes, some of them differ slightly in size. This makes ensuring that there is a snug fit of the mattress in the cot problematic. 

The best thing to do is measure the inside of the cot you are going to use and then look for a mattress that matches those measurements as close as possible. Once you have purchased the mattress, place it in the cot before removing all of the packaging and check that you are not able to fit more than 2 fingers between the mattress and the side of the cot. Also check to make sure that the mattress is not bulging anywhere which may indicate the mattress is too big for the cot.  

A safe cot mattress for your baby


It is suspected that a second-hand mattress may increase the risk of SIDS although it has not yet been proven. Using a mattress for more than one baby is not recommended as the firmness of the mattress decreases over time and may not meet the safety needs for a newborn baby. This is especially true for foam mattresses as they are not as durable as a spring mattress. The American Association of Paediatrics recommends that the cot mattress be replaced with each child. 

A mattress which has not been appropriately stored has a higher chance of containing mould and bacteria from liquids that were not effectively cleaned. 

If you do use a second-hand mattress, try finding one in which a waterproof cover was used. This will help reduce any health risks. The integrity of the mattress should also be checked to make sure it is in good condition with no tears and passes the firmness test. 

Can you use a second hand cot mattress


Keeping your baby’s mattress clean is part of ensuring that their sleep environment is safe. Having a removable mattress cover is helpful as you can pop it into the washing machine and know that it is clean. Some mattresses already come with covers whilst others you can buy separately. 

Once the cover is washed, it is imperative that you check if it has shrunk. A mattress cover that has shrunk will compress the mattress and make it smaller. This can affect how well the mattress fits in the cot and may leave too large of a gap between the mattress and cot side. Always inspect the mattress cover after each wash for loose threads or parts such as zips which may have come loose. 

Whilst there are no specific guidelines on how to wash a cot mattress, Which? suggests the following method: 

Check the manufacturers guidelines as they will indicate the temperature of the water and if a detergent may be used. They indicate that the best way to maintain the integrity of the mattress whilst cleaning it is to vacuum all of the sides. After this you can wipe it down with a damp cloth as directed by the manufacturer. It is then essential that you allow the mattress to completely air dry before covering the mattress with the cover again. This helps prevent any mold or bacteria from growing. 


When a baby is ill or they are struggling with reflux, a parent may be prompted to try and elevate their baby’s mattress by placing a pillow or wedge on top or underneath it. It is, however, advised that parents do not do this as the increased risk of SIDS outweighs any potential benefit of elevating your baby’s mattress. 

We are aware that some Paediatricians in South Africa still recommend elevating the cot to relieve reflux, but it is worth discussing the latest American Association of Paediatrics (AAP) recommendations with your doctor before you decide what to do. 

The AAP indicates that  “elevating the head of the infant’s crib is not effective in reducing reflux”. It also says that your infant will not choke or suffocate if they were to vomit whilst lying on their back as there is a natural reflex which kicks in and protects their airway. 

By elevating the head of your baby’s bed, you also put your baby at risk of sliding to the foot of the cot into a position which can obstruct their airway. Using a wedge or pillow also poses a suffocation risk as these items may cover your infant’s face. 

It is therefore recommended that if you do decide to elevate your baby or use wedges, that you do so with caution. 

Should you elevate a cot mattress

The most important fact to keep in mind when purchasing a mattress for your baby’s cot is to ensure that it is firm enough for your baby and will fit the cot snuggly. By following these two important principles, you are one step closer to creating a safe sleeping environment. 














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