Baby Cot Mattress Safety Guide for UK Parents

Choosing a cot mattress is one of the most important decisions you'll make for your newborn. The right mattress supports safe sleep from day one — and with so much conflicting advice online, it helps to have a clear, UK-focused guide. Here's everything you need to know.

 

What Do UK Safe Sleep Guidelines Say?

The Lullaby Trust — the UK's leading safe sleep charity — recommends the following for cot mattresses:

• The mattress should be firm and flat — not soft, tilted, or wedge-shaped for sleeping
• It should be clean and dry with a waterproof cover
• It should fit the cot snugly with no gaps larger than 2cm around the edges
• Use a new mattress for each baby where possible
• The baby should always be placed on their back to sleep

These guidelines are designed to reduce the risk of Sudden Infant Death Syndrome (SIDS) and should be followed from birth.

Why Firmness Matters for Baby Mattresses

A firm mattress might seem counterintuitive — surely softer is more comfortable? For adults, yes. For babies, no. A soft mattress can conform around a baby's face if they roll or shift position, creating a suffocation risk. A firm mattress maintains its shape and keeps the sleeping surface flat and safe at all times.

To test firmness: press the centre of the mattress firmly with your hand. It should spring back immediately. If it holds the impression of your hand, it's too soft.

 

Why You Should Use a New Mattress for Each Baby

Research cited by the Lullaby Trust suggests that using a second-hand mattress — even from a sibling — may be associated with a slightly increased risk of SIDS. This is thought to be related to bacteria that can build up in used mattresses over time. Whenever possible, use a new mattress for each baby, even if the previous one looks clean and undamaged.

What to Look for in a UK Baby Cot Mattress

1. Firm, Supportive Foam

High-density foam provides the firm, flat surface babies need for safe sleep. It also supports healthy spinal development during those crucial early months.

2. Waterproof Cover

Babies are prone to nappy leaks, milk spills, and general moisture. A waterproof quilted cover protects the foam from bacteria and keeps the mattress hygienic. Look for a cover that is both waterproof and breathable.

3. Removable, Washable Cover

A removable cover that can be machine washed makes it easy to keep the mattress clean without replacing it. Wash regularly — especially after any leaks or illness.

4. Hypoallergenic Materials

Newborns have sensitive skin and developing immune systems. A hypoallergenic mattress reduces the risk of allergic reactions and is particularly important if there's a family history of allergies, eczema, or asthma.

5. The Right Fit

Measure your cot before ordering. The mattress must fit snugly with no gaps larger than 2cm on any side. Common UK cot bed sizes include 120 x 60cm and 140 x 70cm — but always measure your specific cot as sizes vary between brands.

6. Made in the UK

UK-manufactured mattresses are made to British Standards (BS 1877), giving you confidence in the materials, construction, and safety of the product.

How Long Does a Baby Cot Mattress Last?

A good quality cot mattress should last the full duration of your child's time in the cot — typically up to age 2–3. Signs it needs replacing include visible sagging, loss of firmness, persistent odours despite cleaning, or damage to the cover that can't be repaired.

Frequently Asked Questions

Can I use a second-hand cot mattress?

The Lullaby Trust advises using a new mattress for each baby where possible. If you must reuse one, ensure it is from a smoke-free home, has no signs of damage or sagging, and has a clean, intact waterproof cover.

Should I use a mattress protector?

If your mattress already has a waterproof cover, an additional protector isn't necessary. If it doesn't, a fitted waterproof mattress protector is a good idea.

What size mattress do I need for a cot bed?

Measure your cot bed carefully. The most common UK cot bed mattress sizes are 120 x 60cm and 140 x 70cm, but always check your specific cot's dimensions before ordering.

Shop Baby Cot Mattresses at FoamNest

FoamNest stocks a full range of UK-made baby cot mattresses supplied by Rainbow Nursery Goods — with breathable firm foam, waterproof quilted washable covers, and hypoallergenic materials. Available in multiple sizes to fit most UK cots and cot beds.

Our cot and cot bed mattresses

• All baby & nursery mattresses
• Cot bed mattress
• Anti-allergy waterproof cot bed mattress
• Breathable sprung cot bed mattress

Older or non-standard cot? See our made to measure foam mattresses.