Do UK mattresses contain fibreglass
Some do, as a fire barrier, and the practical rule is simple: never remove a mattress cover unless the manufacturer says you can.
The one rule
Do not unzip and remove a mattress cover to wash it unless the manufacturer explicitly says it is removable and washable.
A zip does not mean the cover is meant to come off. On some mattresses it is there for manufacturing rather than for you, and removing it can release fibres from the barrier layer beneath.
Why it is there at all
UK mattresses must meet fire safety regulations. Manufacturers meet them in one of two broad ways: chemical flame retardants applied to the foam and fabric, or a physical fire barrier wrapped around the core.
Glass fibre is one of the materials used for that barrier. It is cheap, it is effective, and it avoids some of the chemical treatments people are trying to avoid. It is sealed inside the mattress and is not intended to be exposed.
Used as designed, a fire barrier is not a hazard. The problems reported are almost entirely from covers being removed.
What happens when the cover comes off
The barrier layer is not built to be handled. Disturbing it can release fine glass fibres, which are light, spread easily through a home, and cause skin, eye and airway irritation.
They are difficult to clean up because they are small enough to become airborne and settle on soft furnishings. The reports that circulate online, mostly from the US market, describe exactly this: a cover washed, fibres released, and contamination spread by a vacuum cleaner.
The failure is the instruction, not the material. A zipped cover with no clear guidance invites people to wash it.
How to check your own mattress
Read the law label and the care instructions. If it says do not remove the cover, that is the answer, and it is frequently there specifically because of this.
Check the manufacturer's website or ask them directly. A brand that publishes its fire barrier material is being straightforward; many do not state it either way.
Do not investigate by opening it. Unzipping to look is the exact action that causes the problem.
Worth knowing: brands vary and some UK brands state they do not use glass fibre, and natural constructions frequently use wool, which is naturally flame resistant and meets the regulations with less chemical treatment. That is the strongest practical argument for wool in a mattress and it is rarely made.
If a cover has already been removed
If you have removed a cover and suspect fibres have been released:
Do not vacuum with a standard vacuum cleaner. It can spread fine fibres through the exhaust rather than capturing them.
Get the cover back on and keep it on, and keep the room ventilated.
Contact the retailer. Your statutory rights are with whoever sold it to you under the Consumer Rights Act 2015, and a product that sheds irritant fibres in normal use is worth raising as a quality issue.
Seek medical advice if anyone has skin, eye or breathing irritation that does not settle, particularly in children or anyone with asthma.
Professional cleaning may be needed for soft furnishings. This is a situation worth documenting with photographs from the start.
Avoiding the question entirely
Use a mattress protector. It washes, the mattress cover does not have to, and it prevents the stains that void most guarantees. This removes the reason people unzip covers in the first place.
Buy a mattress with a genuinely removable, washable cover if that matters to you, and confirm it in writing rather than inferring it from a zip.
Consider wool-containing or natural constructions if you want to avoid both glass fibre and heavy chemical treatment.
Ask before buying. A brand that will answer what its fire barrier is made of is telling you something useful, and so is one that will not.
Related reading
Care without removing the cover
Natural constructions
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Questions people ask
Do UK mattresses contain fibreglass?
Some do, as a physical fire barrier wrapped around the core to meet fire safety regulations. Used as designed it is sealed inside the mattress and not a hazard; the reported problems come almost entirely from covers being removed.
Can I take the cover off my mattress to wash it?
Not unless the manufacturer explicitly says it is removable and washable. A zip does not mean the cover is meant to come off, and removing it can release fine glass fibres from the barrier beneath.
How do I know if my mattress has a fibreglass barrier?
Read the law label and care instructions, and ask the manufacturer. Do not investigate by unzipping the cover, because that is the action that causes the problem.
What should I do if fibreglass has been released?
Do not vacuum with a standard cleaner, which can spread fibres through the exhaust. Get the cover back on, ventilate, contact the retailer, and seek medical advice for irritation that does not settle.