Choosing a baby mattress: what to look for? The complete guide

The checklist in short

• The size fits the cot exactly, with no gaps along the edges.
• The mattress is firm and flat. Your baby's head does not sink into it.
• The mattress is at least 8 cm thick.
• The material lets air through and does not trap heat.
• The cover has a zip, is washable and is not waterproof.
• There are no loose parts your baby could swallow.
• You know which part of the mattress has been tested for harmful substances.
• You place your baby on their back, without pillow, duvet or soft toys.

1. Which size fits the cot?

The mattress must fit the cot exactly: not too long, not too short and without openings between the mattress and the sides. A baby can get an arm, leg or head stuck in a gap. Guides give about 2 cm as the limit: more space than that is too much. Always measure the inside of the cot, even if the size on the packaging matches.

In a crib there is one more thing: the side wall, measured from the top of the mattress, must be at least 20 cm high. A mattress that is too thick or a top layer can reduce that.

2. How firm should a baby mattress be?

Firm and flat. That is the most important feature of a good baby mattress. A mattress that is too soft lets the head sink in, which is a risk for breathing. A mattress that bends increases the chance that your baby ends up between the mattress and the cot. According to experts, the right firmness is also important for the development of the back.

A simple test: press your flat hand on the middle of the mattress. Does it not sink in too far and does it come straight back up? Then it is firm enough.

Preferably choose a new mattress. A mattress that has been used for years may be deformed, and you do not know whether the inside is still in order. If you do have one from an older child, check that it still lies flat, is firm, is undamaged and still fits the cot.

Soft extra mattress toppers and cushions in the cot are not needed for a baby. Adults find soft comfortable, a baby gains nothing from it.

3. How thick should a baby mattress be?

Guides from, among others, Ouders van Nu and babyhelp.nl give a minimum thickness of 8 cm. A thin mattress bends more easily and feels less stable. More thickness does not automatically make a mattress safer: firmness, fit and material matter just as much. Also look at the height of the cot, because a thick mattress reduces the height of the side.

4. Which material do you choose?

The filling determines how the mattress feels, how well it lets air through and how long it keeps its shape. According to research by the Dutch Consumers' Association (Consumentenbond), no filling performs structurally better or worse than the others. It is mainly about the quality: a good mattress of one material beats a poor one of another.

About ventilating top layers. Some mattresses have a 3D top layer with a honeycomb structure for extra airflow. That is handy for hygiene. But newborns cannot regulate their body temperature well yet, and an extra ventilating layer can be too cold for them. Ask your maternity nurse or child health clinic before you choose this.

5. The cover: with a zip, washable and safely finished

All sorts of things happen with a baby: a leaking nappy, spit-up, sweat. A cover you can unzip and wash yourself is therefore no luxury. Pay attention to these points:

• Zip and washable. A removable cover keeps the mattress hygienic. Check the washing instructions. Many guides recommend 60°C, because that kills dust mites and mould.
• Not waterproof. The Consumentenbond advises choosing a cover that is not waterproof or water-repellent. Waterproof layers let little air through and trap heat.
• A sturdy zip. Plastic teeth do not rust. Coarse teeth bend and break less easily than fine ones. A two-part zip lets you wash one half and leave the other on the mattress.
• No loose parts. A baby can swallow small parts that come loose, such as a zip puller. Loose stitching, especially loose nylon thread, is also dangerous.
• An extra layer around the filling. A zip-off cover should come with an inner layer, so your baby can never reach the filling.

6. Do you need a mattress protector?

Not necessarily. Many parents use one against moisture, spit-up and nappies, but the choice is less simple than it seems. In 2019 the Consumentenbond tested fifteen mattress protectors for air permeability. Many waterproof protectors and toppers without a ventilating layer let little to no air through, even when they were advertised as "breathable". A baby then finds it harder to lose heat.

What does that mean for you?

• A good mattress with a washable cover is often better than a mattress with a separate waterproof protector.
• Do you still want a protector? Choose one that lets air through and can go in the washing machine.
• A cotton fitted sheet on the mattress is enough for most babies.
• Never use two or three layers on top of each other. That makes the mattress softer and warmer.

7. Safe sleep: what the mattress does and does not do

A good mattress contributes to safe sleep, but it is only part of the whole. The right size, firmness and a material that lets air through reduce risks. Overheating is mentioned as a possible cause of cot death, which is why breathable support is important.

These basic rules apply to every mattress:

• Place your baby on their back.
• Use their own bed, with a firm mattress and a fitted sheet.
• Keep pillows, duvets, soft toys and other soft objects out of the bed.
• Make sure your baby does not get too warm.

This is general advice. For questions about your baby's sleeping environment you can contact Opgroeien (formerly Kind en Gezin), your child health clinic or your doctor.

8. Smell, certificates and harmful substances

This is a subject many buying guides skip, even though a baby smells and touches the mattress up close for hours a day. A new mattress can have a slight smell at first. Let it air for a few hours in a well-ventilated room before you use it.

Labels can help you compare materials, but always ask which part has been tested: only the core, only the cover, or the whole mattress.

• OEKO-TEX® STANDARD 100 tests materials for harmful substances. Product class I is the strictest class and applies to products for babies and children up to 3 years.
• eco-INSTITUT checks materials for emissions of harmful substances.