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How long does it take a mattress in a box to expand?

When you unbox a mattress, the expansion period allows it to return to the initial shape.

Unboxing the Nectar Classic Memory Foam

it’s possible for you to learn more in our guide tomattresses in a box vs traditional mattresses.

What happens if a mattress in a box doesn’t expand properly?

The materials will still be partly compressed, causing sagging in certain areas.

Two women unpack the Helix Twilight Mattress in a box, still compressed in plastic, onto a bed frame.

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.

The image shows Tom’s Guide’s testers unpacking the Siena Memory Foam Mattress

Why might a mattress in a box not expand properly?

Here’s why your mattress might not have expanded properly…

1.

Most reliable brands avoid this, but be cautious of cheap mattresses with super-fast shipping.

Helix Midnight Luxe Mattress

However, the problem could be with you.

We recommendunboxing your new mattressas soon as possible after getting it home.

When a mattress expands it needs air and space to recover from the compressing process.

A hand tests the temperature control of the 32 Latex Topper

Sometimes, things go wrong.

What can you do if your mattress in a box doesn’t expand properly?

Do this carefully, as you don’t want to risk damaging the mattress and voiding your warranty.

Helix Midnight Luxe mattress…

Take a photo of your mattress before you get started, to prove there was an issue with expansion.

The main culprit is likely the bed frame.

Dressing the bed too early might also have caused issues.

siena memory foam mattress

Improper expansion is likely a structural problem and should be covered by the mattress warranty.

Siena

Plank Firm Mattress - Queen

Plank Mattress

Purple Plus™ Mattress - Queen

Purple

Two testers for Tom�s Guide sat on the Nectar Luxe mattress and smiling at each other

A person sits on the foot of the Leesa Legend Hybrid Mattress on a bed frame, testing the edge support and build quality

Two testers pull the compressed Leesa Legend Hybrid Mattress out of its box

The Siena Memory Foam Mattress in a box on the floor in front of a bed frame, ready to be unboxed

A mattress we tested is dressed with neutral colour bed linens and pillows

A split image featuring the Nectar Classic Memory Foam Mattress on the left and the DreamCloud Luxury Hybrid on the right, leading into the DreamCloud Luxury Hybrid vs Nectar Classic showdown

The image shows a woman sitting up in bed and clutching her shoulder in pain

The Tempur-Pedic Tempur-Adapt mattress on a bed frame in a bedroom, a man and his young sun sitting on top of it, smiling. A Tom�s Guide price drop deals graphic (right)

A couple using the Scandinavian Sleep Method

Bed bugs

The Saatva Murphy Bed Mattress on a Murphy bed frame lying flat, in a bedroom

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Apple iPhone 16 held in the hand.

Ninja Air Fryer

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Lenovo ThinkPad X1 Carbon Gen 13 Aura Edition on a garden table