Mattress Online Rock Hard Super Firm Foam Mattress
Mattress
Mattress Online Rock Hard Super Firm Foam Mattress
Size
Firmness
Firm
Construction
Depth (cm)
23
Layers
Layer Details
- Reflex Foam. A supportive foam that moulds to your body, which means it promotes spinal alignment and a slightly personalised feel despite the very firm surface. It's durable and resilient, holding its shape for an extended period of time.
Layer details from mattressonline.co.uk product page, September 2026.
- Fits the tightest rooms: At 90cm wide, it slots into box rooms, loft conversions with a narrow strip of usable floor, and bedrooms where a desk and wardrobe already claim most of the space.
- Modest room requirement: We suggest allowing at least 2.1m x 2.8m of floor space, which most UK spare rooms and children's bedrooms can manage comfortably.
- Extra-firm support for one: The 23cm reflex foam build gives a solid, stable surface, which means heavier solo sleepers or those advised to sleep firm get proper resistance rather than sink.
- Practical for a spare room office: A single leaves floor clear for a desk, so a study can hold a genuinely supportive guest bed rather than a fold-out compromise.
- Cheap, easy bedding: Standard single sheets and a 135 x 200cm single duvet fit, and both are the most widely stocked bedding of any UK size.
This size suits you if...
You sleep alone and know from experience, or on medical advice, that you need a very firm mattress. Perhaps you're kitting out a spare room that doubles as an office and want a proper mattress rather than a sofa bed, or furnishing a first flat where the frame came with the room. Heavier teens who prefer a firm feel are also a reasonable fit.
Consider another size if...
You're buying for two, or you're a restless solo sleeper who wants more room to spread out. We'd recommend the UK small double instead: it's 30cm wider and the same length, and we suggest a room of at least 2.4m x 2.8m for it.
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Is the Rock Hard Super Firm in a UK single suitable for a child?
We'd be cautious. This is the brand's firmest rating, and lightweight sleepers tend to find extra-firm surfaces unyielding at the shoulder and hip because they don't press into the foam enough to get any contouring. For a heavier teenager who prefers a firm feel it's more sensible; for a young child, a softer single would usually suit better.
What are the dimensions of the Rock Hard UK single mattress?
It measures 90 x 190cm, or 3ft x 6ft 3in, the standard UK one-person size. That's 45cm narrower than the UK double and the same length, so it fits any standard UK single frame or divan. Bedding is straightforward too: standard single sheets and a 135 x 200cm single duvet.
Can I put the UK single Rock Hard on a bunk or mid sleeper frame?
The footprint is right, since bunks and mid sleepers take a standard 90 x 190cm mattress. Depth is the thing to check: at 23cm this is a full-height mattress, and some raised frames specify a maximum depth so the guard rail stays high enough. Check your frame's limit before ordering, particularly for a top bunk.
How much floor space does a UK single need?
We suggest allowing at least 2.1m x 2.8m, which gives you room to walk alongside the bed and open drawers or a wardrobe. That modest footprint is the appeal here: in a child's room competing with toy storage and a desk, or a loft conversion where the slope limits usable floor, a single is often the only size that works.
Should I buy the Rock Hard in a UK single or UK small double?
For a guest room or a growing teenager, the UK small double is tempting: it's 30cm wider than the UK single and the same length, though we suggest a room of at least 2.4m x 2.8m for it. If the room is tight, or you need two beds plus a walkway for siblings sharing, stick with the UK single. Compare the retailers listed on this page for current prices.