We believe parents deserve to know what is inside their baby’s mattress. Foam density and firmness are useful starting points, but they measure different things. Understanding both helps you look beyond a description such as “high density”.
Density and durability
Density is the mass of foam in a given volume. A foam with a density of 22 kg/m³ weighs 22 kilograms per cubic metre.
Density does not tell you how firm the foam feels. When comparing similar foams, a higher polymer density generally helps the material retain its properties through use. The formulation and any added fillers also matter, so density alone is not a complete measure of quality or lifespan.
Firmness and compression
Firmness describes how much force is needed to compress a foam sample under specified test conditions. It may be expressed in newtons, but figures are only meaningfully comparable when the test method and conditions are the same.
For example, compressing a 10 cm sample by 40% reduces its thickness by 4 cm, leaving it 6 cm thick. If the force required in that particular test is 120 newtons, the result is 120 N. The percentage of compression, sample dimensions and testing method must accompany the result for a proper comparison.
In the grading format used here, 22/120 means a density of 22 kg/m³ and a firmness rating of 120 newtons. It does not mean that 120 newtons is a universal pass mark for a baby mattress.
The foam in Gold Sprung
Our Gold Sprung mattress uses 35/135-grade foam around its individually pocketed springs. That means a specified density of 35 kg/m³ and a firmness rating of 135 newtons.
Publishing the grade gives you more information than the words “high density” alone. However, the finished mattress’s construction and safety testing remain essential: a foam specification cannot establish the suitability of the complete mattress by itself.
For further explanation of these measurements, see the Polyurethane Foam Association’s guides to foam performance and foam firmness.
What changed in the fire regulations
On 30 October 2025, mattresses intended for babies and children that are less than 170 cm long and less than 75 cm wide were removed from the scope of the Furniture and Furnishings (Fire) (Safety) Regulations 1988. Both size limits apply.
This exemption does not remove the duty to supply safe products, including consideration of fire safety. General product-safety legislation still applies: the General Product Safety Regulations 2005 in Great Britain and EU Regulation 2023/988 in Northern Ireland.
Appropriate standards, including BS EN 16890 where relevant, can help businesses demonstrate compliance. A standard is not the same thing as the legislation itself.
Read the UK Government guidance on the 2025 amendments for the scope and requirements.
Why the rules changed
The Government’s stated aim was to reduce babies’ and young children’s exposure to chemical flame retardants in products where the risk from that exposure was considered greater than the fire risk. The exemption does not itself establish that a particular mattress contains no flame retardants; check the manufacturer’s material information.
What to look for
Ask for clear material specifications and evidence about the finished mattress. Whatever its core is made from, The Lullaby Trust recommends a firm, flat mattress with a waterproof cover. Check that it fits your cot correctly, follow the care instructions and replace it if it is damaged or no longer provides a firm, flat surface.