The four criteria that determine the choice
A baby mattress should be chosen based on four criteria: the exact dimensions of the bed, firmness, thickness, and certifications. Everything else comes afterward. A mattress that is too soft or does not fit the bed base properly creates a risk instead of providing comfort.
This guide explains each of these criteria in detail, shows you how to check them yourself, and points out marketing claims that add no value. The goal is simple: buy once, buy correctly, and keep the mattress until the child moves to a bigger bed.
What size mattress should you choose for a baby?
The mattress must have exactly the same dimensions as the inside of the bed. In France, the standard cot size is 60 x 120 cm. The other common size is 70 x 140 cm, often chosen to last longer.
The most common sizes
The 60 x 120 cm size remains the standard for a first bed. It fits in a small bedroom and accommodates most fitted sheets on the market. The 70 x 140 cm size provides more space from the age of two, but takes up more room.
Travel cots, on the other hand, use dimensions specific to each model. Never put a standard cot mattress in one: the manufacturer supplies its own, and only that mattress is designed for the frame. Our guide to travel cots explains this point in detail.
The gap between the mattress and the frame
There should be no noticeable gap between the mattress and the bars. The practical rule is simple: if two adult fingers fit easily along one side, the mattress is too small. A gap could allow a baby to slide their head or an arm into it.
Measure the inside of the bed before buying, not the size stated on the packaging. Manufacturing tolerances exist, and one or two centimetres are enough to create a problematic gap.
Why firmness matters more than softness
An infant does not need a soft mattress. They need a flat, firm surface that does not sag under their weight. A surface that sinks can obstruct breathing if the face becomes buried in it.
What health authorities recommend
French recommendations for infant sleep are consistent: a firm mattress that fits the bed, with no duvet, pillow, or cot bumper. We explain these rules in detail in our article on safe infant sleep.
This firmness requirement applies until the age when the child can roll over and sit up unaided. In practice, most parents keep the same mattress well beyond that point, as its firmness remains comfortable for a young child.
How to test firmness accurately
Press down with your palm on the center of the mattress, then release. The surface should return immediately, without retaining the imprint of your hand. Foam that takes several seconds to regain its shape is too soft for a baby's bed.
Beware of so-called memory foam mattresses for children under two. They are designed to conform to the body, which is precisely the effect to avoid in a cot.
What thickness for a baby mattress?
A thickness of 10 to 12 cm is suitable for a standard cot. Below 8 cm, comfort and long-term support deteriorate quickly. Above 15 cm, the bars become insufficiently high as soon as the child stands up.
The clear height between the top of the mattress and the top of the bars must remain at least 50 cm when the bed base is in the lower position. This clearance prevents the child from tipping over the edge at around ten or twelve months.
Foam, natural fibers, or latex: which materials?
High-resilience polyurethane foam
This is the most common choice, and it is a rational one. High-resilience foam with a density of 20 to 25 kg/m³ offers a good compromise between firmness, lightness, and lifespan. Density is the information to look for on the technical data sheet, rather than the foam's commercial name.
A density below 18 kg/m³ indicates entry-level foam, which will sag quickly. This value appears on the manufacturer's technical data sheet, sometimes in small print.
Natural fillings
Coconut, wool, cotton, or bamboo fibers are found mainly in comfort layers or seasonal sides. They regulate moisture well and breathe properly. However, they are heavier, more expensive, and require more thorough airing in the event of a diaper leak.
Latex
Natural latex is durable and naturally ventilated through its air cells. Its drawback is its weight, which makes changing the sheet more difficult. Always check the actual percentage of natural latex: many products combine synthetic and natural latex.
Certifications and emissions: what to check
Labels that are genuinely informative
Three benchmarks are useful. OEKO-TEX Standard 100 regulates harmful substances in textiles and covers. CertiPUR specifically concerns polyurethane foams and their emissions. The labeling of volatile organic compound emissions, mandatory in France, ranges from A+ to C: aim for A+.
None of these labels replaces the others. An OEKO-TEX-certified cover may cover untested foam, and the reverse is also true. The issue of chemical substances in childcare products is covered in detail in our guide on the chemical safety of baby products.
Air out the mattress before the first night
Unpack the mattress at least forty-eight hours before placing the child on it. Leave it in a ventilated room, without a cover or mattress protector. A chemical odor that persists after this period warrants a return to the seller.
This precaution applies to all new bedding. It reduces exposure to the strongest emissions, which occur in the first few days after unpacking.
Crib mattress, changing mat, floor mat: three distinct surfaces
These three surfaces meet different needs and are not interchangeable. The crib mattress is for sleeping: it is firm, thick, and stays in the crib. The changing mat is for diaper changes, with raised edges and a waterproof surface.
The floor play mat, on the other hand, cushions falls during play and motor-skill development. It is thinner, wider, and can be cleaned with a single wipe of a sponge. Our foldable XPE foam baby play mat is designed for this purpose and never replaces a sleep mattress.
To choose by age and available space, browse our range of play mats.
To understand the differences in foam between these products, our guide to foam mat materials and safety details the densities, certifications, and inspection points.
Care and lifespan
A breathable waterproof mattress protector protects the foam from leaks and significantly extends the mattress's lifespan. Wash it at sixty degrees in the event of an accident, and let the mattress dry completely before making the bed again.
Turn and rotate the mattress every two to three months if the model allows it. A well-maintained baby mattress will easily last until the child moves to a regular bed. Signs of wear to look out for include a permanent dip, sagging along an edge, and the appearance of stubborn moisture stains.
Should you buy a second-hand baby mattress?
It is the only piece of baby equipment that we advise against buying second-hand. Foam firmness deteriorates without any visible signs, and the mattress's moisture history cannot be verified. The risk is not offset by the savings.
For everything else, buying second-hand is often an excellent choice. Our article on second-hand baby equipment distinguishes what can be bought without concern from what should remain new.
The most common mistakes
The first is buying the mattress before the bed, then discovering a difference in dimensions. The second is placing a soft mattress topper on a firm mattress, which cancels out the benefit of firmness.
The third is keeping a mattress with a worn-down area because the child does not complain about it. The fourth is choosing based solely on the listed thickness without considering density. These four habits are enough to avoid most bad purchases.
A question about a specific model or dimensional compatibility? Our FAQ page brings together the most frequently asked questions.
