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How to Choose a Safe Cot Mattress

How to Choose a Safe Cot Mattress

Buying a cot and mattress is one of the biggest purchases you’ll make when setting up your baby’s nursery. It’s also one of the most frequently used items with babies sleeping for most of the day when younger and often remaining in their cot until around 3 years of age.  

However, it’s not just cost and longevity you need to keep in mind when choosing a cot mattress, but also the firmness and safety of the mattress. Whilst there are safety standards for household cots in New Zealand and Australia (AS/NZS 2172:2003 Cots for household use) and travel cots, there are no such mandatory safety standard for cot mattresses. Unfortunately you can't assume that cot (and bassinet or moses baskets) for sale in New Zealand are safe to use with newborns.

So we recommend that you do your research before you buy your baby’s mattress. You can check if mattresses have been checked with the standard test to measure the firmness of a mattress (AS/NZS 8811.1:2013 Method 1: Sleep Surfaces – Test for firmness). This will tell you firstly that the supplier takes mattress safety seriously and also that it is safe to use with your baby. Overseas mattresses, such as European brands, may comply with a different safety standard.


How to choose a safe cot mattress for your baby

Firm mattress for baby cot - How to choose a safe cot mattress for your baby

Firmness Testing for Cot Mattresses

Most parents will be aware that baby’s first cot mattresses need to be firm, but how firm is firm? And why does it need to be so firm when as adults many of us like softer mattresses?


Previous studies have linked overly soft infant mattresses with suffocation and it’s easy to see why when you look at the test results below for a soft mattress. A firm mattress will properly support a baby during their sleep and means that if they roll over during their sleep, their nose won’t become cushioned in the mattress, potentially obstructing their breathing.


Once you’re happy with the firmness of your chosen mattress, you should take care not to soften it by adding toppers or sheepskins. We recommended wool underlays for babies older than 6 months only. Waterproof mattress toppers should fit the mattress well and pillows and bumpers should never be placed in the cot due to the suffocation risk.

But if there's no safety standard, how can I actually test the firmness of the mattress?

Ron Somers, Former Director of Epidemiology, SA Health and a researcher behind the standard mattress firmness test explains how companies test the firmness of a mattress and he also shows how to replicate this simply and easily at home, using a few common household items - 12 CD’s (or DVD’s), 2 full 1L tetra pack cartons with a square bottom (eg milk or juice bottles), a ruler and a marker. You can also test how quickly the mattress springs back into shape when pressure is applied. If it springs back quickly this will likely be a safer option than one that isn’t.

Please note that this is an informal testing method for use in the home, but does provide a reasonable result in terms of knowing how safe your baby’s mattress is.

How to choose the right mattress size for your cot


If you’re buying a cot and mattresses separately you will need to choose a mattress that fits the cot frame tightly, with no more than a 2cm gap between the mattress and the cot frame. This is to prevent baby being caught between the mattress and cot.

When buying a cot in New Zealand, it must have a swing tag stating the recommended mattress size for that particular cot, along with the manufacturer’s name and contact details, so you can refer to this when shopping for your mattress. The manufacturer’s recommended sizing information should be permanently marked on the mattress base.

Additionally, the mattress also needs to be the right depth for your specific cot. If the mattress is too deep for the cot, the height of the railings is effectively lowered meaning the baby could fall from the cot. The cot you choose will determine the depth of mattress that can be used safely and this must be stated on the cot when it’s purchased, along with the manufacturer’s name and contact details.

Mattresses should be between 100 and 150mm thick but do not choose a depth greater than the maximum specifed on your cot.

A note on travel cot mattresses

Many parents often comment that the mattresses in portacots are too thin and not comfortable for baby. They are designed this way to be easy to travel with, and also to ensure a firm sleeping surface for babies and no risk of suffocation between the mattress and sides of the travel cot.

NEVER use any additional mattresses with a travel cot as it’s simply not safe.

Your travel cot will no longer comply with the safety standard if you add any additional mattress and it can create a suffocation risk that has resulted in baby deaths.

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What type of mattress should I choose?

Whether you choose a foam, latex, polyester, wool or innerspring mattress is personal choice, as long as it’s firm enough and leaves only a small gap each side of the mattress, the material does not otherwise affect the safety performance.

There are a number of things to consider when choosing what type suits you.

Innerspring mattresses

  • These tend to be firmer than latex/foam mattresses
  • They tend to last longer, so if you plan on using your mattress for more than one baby this may be the best option for your family

Latex/Foam mattresses

  • These tend to be lighter weight than innerspring mattresses
  • They may lose their shape more quickly than an innerspring mattress
  • You will need to pay close attention to airing your mattress very regularly

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More helpful cot mattress tips for newborns

  • Never wrap your mattress in plastic, all it needs is a waterproof mattress protector and fitted sheet.
  • Always use the mattress without added padding or sheepskins. We recommend wool underlays for babies older than 6 months of age.
  • Never use pillows, bumpers or other loose bedding in the cot as this can pose as a suffocation risk.
  • Position the mattress flat rather than elevated. A cot mattress should only be slightly elevated with medical advice and only by raising one end of the cot slightly, not the mattress

References: "Gilmour, K. (2020) 'How to Buy a Cot Mattress', Choice Buying Guide, 22 September. Available at: (Accessed 8 November 2021).