What to Do When Your Memory Foam Mattress Corners Are Not Expanding? [2023 Update]

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Written by: Alex Savy
Read 7 minLast updated on February 22, 2023

These days, shopping for a new mattress is quite convenient, especially with so many bed-in-a-box options. 

However, receiving a mattress compressed in a box can have its drawbacks, one of them being an improper expansion.

So, if your memory foam mattress corners are not expanding, read this guide to find out how to fix that issue.

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Why Isn’t My Memory Foam Mattress Expanding?

Memory Foam Mattress Expanding

When your new mattress doesn’t expand properly, there can be various reasons behind it, including the following:

  • You left it in the box for too long. Usually, manufacturers recommend users to unpack their new mattresses within the first 72 hours. Leaving your mattress compressed for too long can cause expansion issues.
  • It needs more time. Typically, memory foam takes up to 72 hours to expand fully (1). Therefore, if it’s only been a few hours after you’ve unpacked the mattress, don’t rush. The corners might expand later.
  • It’s too dense (or too thick). Thicker mattresses usually take longer to expand. The same rule applies to the ones using denser foam.
  • Your room is too cold. The visco-elastic chemicals in memory foam are temperature-sensitive. They become more fluid when the heat is applied. This means, leaving your mattress in a cool room will make it expand slower.
  • Your mattress is defective. Sadly enough, some memory foam mattresses (especially cheap ones) often arrive defective. They can be lumpy or have flat edges and corners that don’t expand even after a few days.

Which Mattress Type Takes Longer to Expand? (Quickest to Slowest)

Different types of mattresses are more or less prone to having saggy corners after removing them from the box.

Let’s take a look:

  • Innerspring mattress. This mattress typically doesn’t have many foam layers, so once you remove it from the box and rip the vacuum seal, it expands pretty quickly. Plus, its coil block is typically reinforced on the edges, preventing sagging and ensuring good edge support.
  • Hybrid mattress. A hybrid mattress also has coils, and sometimes it’s more than one layer, so it tends to expand pretty well. Additionally, hybrids are thicker, and extra thickness creates more resistance in the compressed state, which also helps with expansion.
  • Latex mattress. Latex mattresses have a naturally spongy texture, and once they’re released from the box, they quickly spring back in shape. Softer latex might need a bit more time to expand, but overall, it’s uncommon for a new latex mattress to sag.
  • Memory foam mattress. Modern memory foam mattresses need from 6 to 24 hours to expand appropriately. However, cheaper mattresses or models made of traditional viscous memory foam might take longer than that or initially come with saggy corners. So if you purchase such a mattress, this is one of the possible risks.

What to Do When Your Mattress Corners Don’t Expand

What to Do When Your Mattress Corners Don’t Expand

Here’s the deal:

Even if your new mattress doesn’t expand properly, some steps may help you fix the issue. Here’s what you can try:

  • Put it on the floor. If your bed frame isn’t suitable for a memory foam mattress, this may cause uneven expansion. Try putting the mattress on the floor and give it a bit more time to expand. However, make sure that your floor is clean and nothing is lying around there. The thing is, many foam mattresses contain fiberglass that can escape if the cover gets punctured. That might be dangerous, so just to be on the safe side, vacuum the floor thoroughly before putting your mattress there to expand. You might also want to look at some of the best memory foam mattresses without fiberglass for safer use.
  • Return your mattress. If your mattress doesn’t expand fully within the first week, chances are it’s defective. In this case, the best solution would be to return it and pick a better quality model (which you can find here, among the best memory foam mattresses). Consider Nectar if you are looking for a good value for money. This mattress uses quality components and offers a universally comfortable medium feel. And if you are having doubts concerning memory foam altogether, you can also check some of the top mattresses without memory foam that do not typically have issues with the expanding process.
  • Warm the room up. Warmth encourages memory foam expansion. Therefore, you can change your thermostat settings to at least 68 degrees Fahrenheit (or more) to help your mattress corners expand. Some of the online experts advise using steam on mattress corners when they don’t expand fully. And while this trick might be effective (as the steamer will warm up the foam), I would not recommend doing that. The thing is, using a steamer near your new memory foam mattress can lead to moisture accumulation. And that can lead to a series of issues, including mold growth and dust mites.
  • Massage the mattress. No matter how ridiculous it may sound, giving your mattress a massage by rolling on top of it may help. You can also walk on it for around 10-20 minutes (but make sure that your feet are clean).
  • Open the windows. Promoting air circulation can help your mattress expand fully (2). You can open the windows and create a draft in the room, which may also help with off-gassing. Placing a fan near the mattress is another option you can try.

A quick note: if your memory foam mattress is defective, does not expand no matter what you do, and the trial period is over so you can’t return it, you might need to compress your memory foam mattress back for easier transportation (if you decide to donate or recycle it). You can also order a pick-up service, but those can be quite pricey sometimes.


There’s nothing more annoying than flat corners in your new memory foam mattress.

Of course, there’s a chance to fix the problem. Give your new mattress a bit more time or try a few tricks from the list above. 

Keep in mind that in some cases, returning the bed can be a better option. Higher quality mattresses are less likely to have issues with expansion and can guarantee your peace of mind.

What do you think? Will you try to fix your mattress? Or are you ready to exchange it for a better one? Let us know in the comments!


  1. Gail Delaney (2017, July 18). How to Expand Memory Foam. Retrieved from
  2. Emma Williams (2019, October 18). Can You Sleep on Memory Foam Before 24 Hours? Retrieved from


  1. I niughta 12in pillow top hybrid mattress. A week ago it had lumps in it? What to do about it?

    1. Hello Edward,

      Sorry for missing your comment!

      In this case, the best idea would be to contact the manufacturer or the seller. Either the in-home sleep trial or the warranty should allow you to return a mattress that has developed lumps so prematurely.

  2. My memory foam was delivered Monday it’s now Wednesday July 28th. The corners at head board and corners at foot board are not expanding. What to do?

    1. Hi Betty,

      Sorry for the late response.

      In this case, your mattress probably hasn’t had enough time to expand fully. Often, it takes more than 3 days, so I would suggest you wait a little bit longer. After that, you might want to contact the seller and share your concerns. After all, there’s always a chance you’ve received a defective mattress, which should be exchanged in this scenario.

  3. Just brought two xl twin memory foam mattresses. Both are 12″ inch I checked the tags. One expanded to 13″? And the other 11 1/2! Only been 2 hours but a little worried.

    1. Hi Susan,

      Sorry for the late reply! Typically memory foam mattresses need a minimum of six hours to fully expand, so I would give the 11 and a half inches mattress a bit more time. If it is still short, I suggest warming up the room or walking on the mattress to encourage the foam to expand fully. And regarding the 13-inch mattress, it should even out after a few nights of use, and having it a bit taller won’t affect its sleeping performance.

  4. I brought a northern night hybrid king size mattress close to 6 month ago and never took it out the box do you think there a chance it’s damaged?

    1. Hi Wendy,

      Sorry for the late reply! Depending on the brand, some mattresses can handle being in the box longer than others. I would check with the manufacturer directly to see if they have any information on their site regarding this, and remove it from its box as soon as possible to see if the mattress expands properly.

  5. I just got a 12 inch memory foam mattress and when I took it out of the box ,same day I got it, there was a crease all the way down the bed about 1/3 of the side of the bed, and after already 50 hours of letting it fluff up the crease has not gone away. Is it a bad mattress?

    1. Hi Jared,

      Apologies for the late reply! If you’ve tried all the tricks mentioned above, like walking over the mattress and warming up the room to encourage it to expand fully, I would suggest getting in touch with the manufacturer and explaining the situation, as mattresses should not have a crease when you go to sleep on them.

  6. If Your Memory Foam Mattress is expanding Place it on the floor. If your bed frame is not suitable for a memory foam mattress, this may result in uneven expansion.

    1. Hi Citrus Sleep,

      Apologies for the late reply, thank you for your insightful comment. I agree with you.

  7. My nectar king mattress was delivered and set up sunday, it’s now Wednesday and the center has yet to expand. Head and foot area are higher than the center.

    1. Hi Erika,

      Apologies for the late reply. If your mattress is having a tough time expanding evenly, I would suggest trying the tricks mentioned above, like walking along the top to encourage it to even out. If all else fails, get in touch with the manufacturer.

  8. I’ve got a subrtex mattress topper having problems one side has risen but the two ends and the one side is still the same flat T tbs edges ? What do ?

    1. Hi Alison,

      Thanks for reaching out! If you’ve let the mattress expand for at least 72 hours or however long the manufacturer has recommended, as well as tried the tricks I mentioned above, like warming the room up and walking along the mattress to even out the areas, I would get in touch with the manufacturer.

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