Can you sleep on a mattress while it's expanding? We asked Helix, Purple, Emma and more

A man and a woman remove a Purple mattress from its packaging before it starts to expand, ready for sleeping on later
(Image credit: Purple)

Can you sleep on a mattress while it's expanding is one of the most frequent questions we get asked. And we understand why — you want to try out your new bed as soon as it arrives on your doorstep, especially if you're no longer be able to sleep on your old one or your current bed is super-uncomfortable. 

However, nearly all of the best mattresses you can buy online are tightly compressed with a heavy weight then neatly packaged into a box for shipping. That means you'll have to wait for them to fully expand at home once opened.

While it's likely that you've thought about sleeping on your expanding mattress right away, is this any good for you and the bed? If not, how long do you have to wait until your mattress is fully expanded and ready to sleep on?

We asked some of the best mattresses in a box brands — including Purple, Zinus, Simba Sleep, Emma Sleep, Cocoon by Sealyand Brook + Wilde Sleep — to see if you can sleep on a mattress while it's expanding. We also asked how you should set up a mattress-in-a-box, how long their mattresses take to expand, and what you should do if your new mattress doesn't seem to be expanding at all. Here's what they told us...

Can you sleep on a mattress while it's expanding? 

If you want to know whether you can sleep on a mattress while it's expanding, the majority of the mattress brands we've spoken to give a firm "No". "We would advise against it," says a spokesperson from Brook + Wilde Sleep, "just to allow the mattress to reach its full potential."

So, how can sleeping on an expanding mattress stop it from reaching its full potential? "Applying additional pressure will not allow the mattress to fully expand," sleep experts at Cocoon by Sealy tell us. 

Emma Comfort Mattress placed on a bed base in an elegantly furnished room after the mattress has fully expanded ready for sleeping on

(Image credit: Emma Sleep)

Meanwhile, Emma Sleep's Paulina Méndez Robles also points out that memory foam mattresses in particular need the extra time between unboxing and sleeping. Here's why: "Foams can have some trouble recovering. Our mattresses are folded and roll-packed, and this process compresses the foams to very thin layers and that's why a certain amount of time is needed to have them fully recovered," she explains. 

"If you sleep or lay on the mattress for a long time during this process, you can compromise the recovery of the foams. Putting weight on them means they will take the form of your body instead of recovering to the original shape. However, there is no risk to the sleeper in any form."

"For Purple mattresses, we would like to give the mattress six hours to expand before sleeping on it," says Kristen Olson-Turner, Sr. Director of Product Merchandising at Purple. 

"For other mattresses, the expansion of the mattress also allows for mattress off-gassing for the foam. If you sleep on it before it fully expands, the off-gassing smell might be distracting or challenging to achieve a good night of sleep."

Comfy from the first night

However, some brands such as Simba and Zinus, are more lenient about sleeping on a mattress while it's still expanding. "With any Simba mattress, you can sleep on them and still feel the difference from the day it arrives," says Graham Paddon, Head of Contact Centre at Simba Sleep. "The same applies to our toppers."

Stephany Aubrey of Zinus says that, while you need to let the mattress decompress and breathe a little before you start sleeping in on it, you shouldn't leave it too long. "But as part of this process, we recommend that you sleep on it the first night it’s with you to get the air flowing throughout the mattress," she says. 

"However, the following night, you should sleep on your old mattress – if it’s safe to do so – to give your mattress a little more time to complete the decompression process before you begin sleeping on it permanently.”

How long does it take for a mattress to expand?

Okay, so the majority of brands say to wait until your mattress expands before even attempting to sleep on it, but how long will this take? "The rate of expansion is dependent on the components of the mattress, humidity, and temperature in the room, as well as how long the mattress has been compressed and/or rolled," says Olson-Turner from Purple Mattress. 

A woman sleeps on a Purple mattress after it has fully expanded

(Image credit: Purple)

“As soon as your mattress arrives, it’s recommended that you open the box within 72 hours of receipt," says Aubrey from Zinus. "Leaving it cooped up for too long may lead to an extended recovery time."

If you're also wondering what the ideal temperature is to help your mattress expand faster, you may want to turn up the heat and turn on the de-humidifier. "A warmer, dryer room will help your mattress to expand quicker," says the Brook + Wilde Sleep team. 

The bed specialists at Cocoon by Sealy also say that low temperatures can slow down the recovery process. "We recommend letting our Cocoon by Sealy Chill mattress expand for 4 hours at room temperature. With colder weather, we recommend giving it 24 hours to fully expand without sleeping on it. 

"When the temperature is colder the material is more compact and firmer. When the temperature is warmer the material is softer."

Aubrey says that the bed's preference for warmer temperatures is called thermal expansion. "By keeping your bedroom at around 21°C or warmer, you can encourage the molecules in your new mattress to move around.

"This can help to expand your mattress, encouraging it to plump up to a nice, firm level. If your home isn’t quite this warm or if you live in a colder climate, adding a portable heater to the bedroom (at a safe distance from your mattress) can be helpful.” 

Here's a brand-by-brand break down of how long it takes for your new mattress to fully expand, according to each of the brands' experts:

  • Simba: a Simba mattress can be slept on within 3 to 6 hours after unboxing, but could take up to 72 hours to fully expand
  • Zinus: between 48 and 72 hours
  • Purple: 24 hours
  • Cocoon by Sealy: 4 to 24 hours
  • Brook + Wilde Sleep: 4 to 6 hours
  • Emma: 24 to 72 hours

How long does it take a memory foam mattress to expand?

While temperature can play a key part in how long it takes for your bed to expand, the material of your mattress is also a huge factor. Memory foam beds, for example, tend to take longer to expand than innerspring or hybrid beds.  

"Memory foam will take longer to expand than a hybrid mattress since foam doesn’t expand as quickly as coils," says Olson-Turner. "Purple mattresses will take 24 hours to fully expand. However, some memory foam mattresses will take longer to expand, especially if they include more temperature sensitive foam, if they are made overseas, and have been compressed and/or rolled longer."

Woman with arms in the air stretching on her bed with back to the camera as she wakes up from sleep

(Image credit: Getty images)

To help speed up your memory foam bed's full expansion, Aubrey recommends walking over it. "Once removed from its packaging, help air flow through your mattress by rolling or walking on it," she advises. "This movement will encourage tiny air pockets to open up and expand, helping to speed up the process."

My mattress isn't expanding. What should I do?

Mattress brands advise you call their customer service department if your bed isn't expanding — but only after a certain amount of time. Simba, Zinus, and Emma recommend waiting at least 72 hours after unboxing to contact their customer services.

Other brands however say that you should take action sooner. Purple, for example, advises to leave at least 36 hours after unpacking, while Cocoon by Sealy and Brook + Wilde Sleep each say you should contact them after 24 hours.

Frances Daniels
Sleep Staff Writer

Frances Daniels recently joined the Tom's Guide team as Sleep Staff Writer, and her role includes covering all sleep and mattress news, in addition to mattress reviews and buyer's guides. Frances is a PPA-accredited journalist and is hugely interested in the relationship between good sleep and overall health. When not writing about sleep and mattresses for Tom's Guide, Frances enjoys writing about women's issues, health and wellbeing, the environment, and her native Wales.