Mattresses in a box have revolutionized the sleep market, getting mattresses to your room without a delivery team maneuvering your doorways. But compressing a mattress into a box means it needs to decompress at the other end — what do you do if your mattress doesn't expand properly?
We've tested numerous beds in a box to find this year's best mattresses, and our team rarely encounters problems with expansion. However, making a mattress is a complicated process and you might find after unboxing your mattress hasn't sprung into the shape you imagined.
This doesn't necessarily mean you have to throw the whole bed away, but if you've chosen the best mattress in a box for your sleep style, you want to ensure you're getting all the comfort and support you paid for. Here's why a mattress might not expand properly and what you can do about it, so you can shop the Presidents' Day mattress sales with peace of mind.
How long does it take a mattress in a box to expand?
When you first release a mattress in a box from its plastic packaging there's a sudden moment of expansion — the mattress will often grow several inches in a few seconds. After that initial decompression most mattresses need at least several hours to reach their full height, and it can sometimes take multiple days for a mattress to expand.
Mattresses in a box are compressed, sealed and rolled, to ensure they can fit into a small(ish) package. When you unbox a mattress, the expansion period allows it to return to the initial shape. On the other hand, traditional mattresses, which are delivered flat, should be ready to sleep on straight away. You can learn more in our guide to mattresses in a box vs traditional mattresses.
What happens if a mattress in a box doesn't expand properly?
If a mattress in a box hasn't expanded properly it won't provide the level of support and comfort that you need. The materials will still be partly compressed, causing sagging in certain areas.
This sagging doesn't just look bad, it can also lead to discomfort and pain. When a mattress sags it loses support, causing the body to sink into the dips. This then puts pressure on the muscles, leading to aches and pains.
Why might a mattress in a box not expand properly?
Mattresses in a box generally finish expanding within a few days, but on rare occasions, you might feel your mattress hasn't reached its full potential. Here's why your mattress might not have expanded properly...
1. It needs more time
Mattress decompression can take anywhere from a few minutes to a few days, so if you're wondering why your bed is looking a little droopy, it might be that it's still finishing up. Hold tight and double check the manufacturer's instruction, to ensure you're familiar with the suggested waiting period.
2. It's spent too much time in the box
Compressing and rolling shouldn't damage the mattress, as the materials are strong enough to withstand the process. However, leaving a mattress in a box too long can cause the interior layers to become compromised, meaning when the mattress is unwrapped, it can't full expand. For more information about how long mattress from different brands can stay unboxed, visit our guide on how long mattresses can stay in a box.
This might be the fault of the manufacturer, as ready-made mattresses can sometimes be left in the box on the warehouse floor for months. Most reliable brands avoid this, but be cautious of cheap mattresses with super-fast shipping.
However, the problem could be with you. While waiting for the room to be ready / a house move / a spare 20 minutes to unbox, your mattress is tuck curled up in the box, causing the materials to degrade. We recommend unboxing your new mattress as soon as possible after getting it home.
3. It's on the wrong bed frame
What goes under your mattress impacts the feel of your bed, and the wrong bed frame might be the reason why your mattress won't fully expand. Mattress slats should be no more than three inches apart, to prevent the mattress from sagging into the gaps.
4. You slept on it too soon
Can you sleep on a mattress while it's still expanding? It's not recommended, so you need to have some patience. When a mattress expands it needs air and space to recover from the compressing process. Sleeping on the mattress as it decompresses applies pressure to the already vulnerable foams, which can cause them to remain decompressed.
The best way to avoid this is to simply resist sleeping on your mattress until it's past the recommended expansion phase. And while we all enjoy jumping on a brand new bed, holding back will deliver more comfort in the long-term.
5. It's defective
There are a lot of steps involved in making a mattress, from coiling the springs of the best hybrid mattresses to slicing the foams. Sometimes, things go wrong. While trusted brands rarely allow a defective mattress to make it to your home, one or two do occasionally slip through the cracks.
What can you do if your mattress in a box doesn't expand properly?
One quick note from a team that has tested a lot of mattresses: a mattress in your home rarely looks as good as it does online. That doesn't mean you have to put up with a bad bed, but don't be surprised if your new mattress can't match the dazzling appeal of the brand listing.
1. Try manipulating the foam
Many mattresses use foams in the upper layers to add cushioned comfort, and this foam is often slow to expand — particularly at the corners, where the mattress has been heavily compressed. If the foam has gotten stuck during the expansion phase, a helping hand can gently tease it into the corners.
Do this carefully, as you don't want to risk damaging the mattress and voiding your warranty. Take a photo of your mattress before you get started, to prove there was an issue with expansion.
But if your brand new best memory foam mattress is showing large dips across the surface of the bed, it's unlikely you'll be able to cajole the foam into place.
2. Reassess your sleep setup
The problem might not be with your mattress but with the rest of your sleep set-up. The main culprit is likely the bed frame. If the slats are too wide or you're using a box spring with an incompatible mattress, it could be hindering your mattresses ability to expand.
Dressing the bed too early might also have caused issues. Some of the best pillows can be pretty heavy, so if you tossed one on the head of the bed as the mattress expanded, you might have impaired decompression. And it sounds like a silly thing, but if your mattress is looking squashed at the corners, make sure your sheets aren't too tight.
3. Contact customer services
If you've waited the recommended time and your mattress still hasn't expanded, then contact the brand's customer service line. Improper expansion is likely a structural problem and should be covered by the mattress warranty. The helpline should be able to advise you on next steps, including if your eligible for an exchange or a refund.
