The four criteria that determine the choice
A baby mattress should be chosen based on four criteria: the bed's exact dimensions, firmness, thickness, and certifications. Everything else comes afterward. A mattress that is too soft or poorly fitted to the bed base creates a risk instead of providing comfort.
This guide details each of these criteria, explains how to check them yourself, and highlights sales arguments that add no real value. The goal is simple: buy once, correctly, and keep the mattress until the child moves to a larger bed.
What dimensions should you choose for a baby mattress?
The mattress must exactly match the bed's interior dimensions. In France, the standard size for a cot 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 offers more room from the age of two, but takes up more space.
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 the travel cot explains this point in detail.
The gap between the mattress and the frame
There must be no significant space between the mattress and the bars. The practical rule is simple: if two adult fingers can easily fit along one side, the mattress is too small. A gap can allow a baby to get their head or an arm caught.
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 sink under their weight. A surface that sinks can hinder breathing if their 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 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 independently. In practice, most parents keep the same mattress for much longer, as its firmness remains comfortable for a young child.
How to test firmness accurately
Press your palm into the center of the mattress, then release it. The surface should return to its original shape immediately, without retaining the imprint of your hand. Foam that takes several seconds to regain its shape is too soft for a baby's cot.
Be wary of so-called memory foam mattresses for children under two. They are designed to contour to the body, which is precisely what should be avoided 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 durability deteriorate quickly. Above 15 cm, the bars become too low as soon as the child can stand.
The clearance between the top of the mattress and the top of the bars must remain at least 50 cm when the bed base is in its lowest position. This margin 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 for good reason. High-resilience foam with a density of 20 to 25 kg/m³ offers a good balance between firmness, lightness, and durability. The density is the information to look for on the technical specification sheet, rather than the foam's commercial name.
A density below 18 kg/m³ indicates an entry-level foam that will sag quickly. This figure appears on the manufacturer's technical specification sheet, sometimes in small print.
Natural fillings
Coconut, wool, cotton, or bamboo fibers are mainly used as a comfort layer or a seasonal side. They regulate moisture well and allow adequate airflow. However, they are heavier, more expensive, and require more thorough airing if the diaper leaks.
Latex
Natural latex is durable and naturally ventilated through its 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
The labels that provide genuinely useful information
Three guidelines 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 discussed in detail in our guide to chemical safety in baby products.
Air it out before the first night
Unpack the mattress at least forty-eight hours before putting the child down on it. Leave it in a ventilated room, without a cover or mattress protector. A chemical smell that persists after this period warrants returning it to the seller.
This precaution applies to all new bedding. It reduces exposure to the highest emissions, which occur in the first few days after unpacking.
Crib mattress, changing mat, play 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 cushions falls during wakeful play and motor development. It is thinner, wider, and can be wiped clean with a sponge. Our foldable XPE foam play mat serves this purpose and never replaces a sleep mattress.
To understand the differences between the foams used in these products, our guide to foam mat materials and safety details the densities, certifications, and points to check.
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 larger bed. Signs of wear to watch for include a permanent indentation, sagging along an edge, and the appearance of stubborn moisture stains.
Should you buy a second-hand baby mattress?
This is the only baby-care product we advise against buying second-hand. Foam firmness deteriorates without visible signs, and the mattress's history of exposure to moisture cannot be verified. The risk is not offset by the savings.
For everything else, second-hand is often an excellent choice. Our article on second-hand baby products distinguishes what can be bought with confidence from what should remain new.
The most common mistakes
The first is buying the mattress before the bed, then discovering a size mismatch. The second is placing a soft mattress topper on a firm mattress, which defeats the purpose of firmness.
The third is keeping a mattress whose foam has developed a hollow because the child does not complain about it. The fourth is choosing based solely on the stated thickness without considering density. These four habits are enough to avoid most poor purchases.
A question about a specific model or size compatibility? Our FAQ page brings together the most frequently asked questions.
