How long does a rolled mattress take to expand, and when is it a fault?
You have cut the wrapping, it has unrolled with a hiss, and it is lying there at half height looking like a deflated lilo. This is normal. Here is what happens next, how long it takes, and how to tell the difference between "give it time" and "send it back".
What is happening
The mattress was compressed in a press to a fraction of its height, rolled, and vacuum-sealed, often weeks ago. The foams have been held squashed for that whole time, and the springs bent round a tube. Once the bag is cut, air gets back into the foam cells and the springs straighten. Foam recovers quickly at first, then slowly; the middle of the roll, which was compressed hardest and longest, takes longest.
How long
| Time since unboxing | What to expect |
|---|---|
| 10 minutes | Roughly two-thirds of full height |
| 2 to 6 hours | 80 to 90 per cent; you can lie on it to test the feel |
| 24 hours | Most mattresses are at full height; makers usually say sleep on it from here |
| 48 to 72 hours | Memory-foam-heavy and thicker mattresses reach full height |
| 7 days | Anything still short, dished or lumpy after this is not going to recover |
Cold slows it down. A mattress unboxed in a cold room in winter can take a day longer; a warm room helps. Walking gently on it or rolling on it helps too.
The smell
New foam off-gasses as it expands: a chemical, slightly sweet smell, strongest in the first day, gone within a few days with the window open. It is unpleasant and, for foams certified under CertiPUR or similar, not harmful. Strong smell after a week, or a smell that gives you a headache, is worth reporting. Latex has a faint rubber smell that fades more slowly.
What is normal
- Slight unevenness in the first day.
- Faint creasing across the top from the roll, which drops out.
- A little less height than stated (up to about a centimetre) after 72 hours, because stated depths are often the pre-compression measurement.
- Firmer than expected for the first two to four weeks while the foams loosen.
What is a fault
- More than two centimetres short of the stated depth after a week.
- A dip or ridge along the line of the roll that does not flatten after a week: a compression set in the foam.
- Lumps or a visibly uneven surface after a week.
- Springs you can feel through the top as distinct points.
- A torn cover or a burst seam on unboxing.
Photograph it with a tape measure in shot, and contact the seller within the 14-day period if you can; a compression set is a manufacturing fault and is covered under the Consumer Rights Act regardless of any trial terms. See your return rights.
Why it varies so much
Lower-density foams (under 40 kg/m³) can take a permanent set when compressed for a long time, which is why cheap boxed mattresses are the ones that arrive short. Higher-density foams recover. Springs of standard gauge recover; the thinnest wire can stay bent. A mattress that has sat compressed in a warehouse for months is more likely to have a set than one boxed last week, and you cannot tell which you have got.
Unboxing properly
- Get it into the bedroom in the box; it is far easier to carry rolled.
- Cut the outer plastic, unroll it on the base, then cut the inner seal with the mattress flat and square on the base; it expands fast.
- Leave it uncovered, window open, for the first day.
- Do not put a plastic-backed protector on it for 48 hours; let it breathe.
- Keep the box until you are sure, in case of a return.
The other way
Some mattresses are not rolled at all. A flat-delivered mattress arrives at full height, with no waiting, no smell to speak of and no possibility of a compression set, and it can be built with heavier springs and natural fillings that a roll would ruin. It costs more to deliver. See rolled vs flat-delivered for the trade-off. Every Chapter mattress is delivered flat by two people for exactly this reason.
The short version
- One to three days to full height; sleep on it after 24 hours.
- Faint smell for a few days is normal.
- Short by over 2 cm, a dip along the roll, or lumps after a week: a fault. Photograph, report.
- Cheap low-density foam is the mattress that arrives short.
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