Assembly guide

Mattress in a box

Not really assembly, but the part everyone gets wrong. Cut it in the right place and let it breathe.

Time15 minutes
People2 needed
Difficulty●○○○○
Walkthrough3:00 video

Not what you bought? Try Metal platform bed frame · Upholstered or wooden bed with a headboard

What you need

In the box already: Nothing. It is a mattress.

Before you open anything

  • Get the box into the bedroom before you open anything. An expanded mattress will not go through a doorway comfortably and cannot be re-rolled.
  • Have the bed frame finished, slats in, and the floor clear.
  • Open a window. New foam has an off-gassing smell for the first day or two, which is normal and fades.

Please don't skip these

  • Cut the inner bag with a shallow, slow stroke. A knife that reaches the foam leaves a permanent slice.
  • Never let anyone stand near the open end as you cut the vacuum seal. It expands fast and with force.

The whole thing, step by step

9 steps

  1. Get the box into the room first

    Carry or drag the box all the way to the bedroom while it is still compressed. This is the only chance you get.

    • Two people, use the handles if there are any
    • Slide it on cardboard if the hallway is tight
    • Position it next to the finished bed frame
    Watch out. Once expanded it cannot be put back in the box. Doorways, stair turns, and tight landings must be dealt with now.

  2. Open the outer box and get it onto the frame

    Cut the box open and lift the still-wrapped roll onto the bed frame. It is much easier to manoeuvre compressed than expanded.

    • Cut the box, do not tip it out
    • Lift the wrapped roll onto the slats
    • Lay it along the frame in the direction it will unroll
    Tip. Note the 'head' and 'foot' or 'this side up' markings on the plastic before you cut. They matter on hybrids and pillow-tops.

  3. Unroll it before you cut the vacuum bag

    Take the outer plastic off and unroll the mattress flat on the frame, still inside its vacuum bag. Only then do you cut the seal.

    • Remove the outer loose plastic
    • Unroll the sealed mattress flat on the frame
    • Center it before cutting anything
    Watch out. Cutting the vacuum bag while it is still rolled up means wrestling an expanding mattress across the room. Flat first, then cut.

  4. Cut the vacuum seal shallow and slow

    Cut the inner bag along the top surface with a shallow stroke. Scissors if you can get them in. You will hear the air rush in.

    • Cut along the top face, not the edge
    • Shallow, slow, with the blade angled away from the foam
    • Step back as it inflates
    Watch out. A slice in the foam cannot be repaired and most warranties will not cover damage from opening. Go slowly — this takes ten seconds and lasts ten years.

  5. Pull the bag out from underneath

    As it rises, work the plastic out from under it. Easier if you do it while it is still only partly expanded.

    • Pull the bag out one end at a time
    • Lift a corner of the mattress as needed
    • Get all the plastic clear before it is fully risen
    Tip. If you miss a piece of plastic and it ends up trapped, two people can roll the mattress on its side to retrieve it.

  6. Let it expand and air out

    It takes a couple of hours to reach most of its height and up to two days to fully firm up. Leave it bare with the window cracked.

    • Leave it uncovered for a few hours at least
    • Window open if you can
    • No sheets, no mattress protector yet
    Tip. If it still looks a little thin or has a soft spot after a day, give it another day. Foam genuinely does keep recovering.

  7. Check it is actually supported

    Foam mattresses need slats close together or a solid base. Wide gaps make the foam sag between them and will void the warranty.

    • Check the gap between slats against the mattress warranty, usually around three inches maximum
    • Add extra slats or a bunkie board if the gaps are too wide
    • Make sure every slat contacts the frame
    Watch out. This is the most common cause of a foam mattress 'going bad' in year one. The mattress was fine; the base was not.

  8. Protector on, then sheets

    Once it has aired out, put a protector on before anything else. Most warranties are void on a stained mattress.

    • Waterproof or breathable protector first
    • Then the sheets
    • Note the warranty registration if there is one
    Tip. Take a photo of the law tag on the side of the mattress. Warranty claims need that model and date information and the tag is easy to lose track of.

  9. Give it three weeks before you judge it

    New foam feels different for the first few weeks and your body also adapts. Most sleep trials are long for exactly this reason.

    • Sleep on it for at least two to three weeks
    • Note the trial period end date somewhere
    • Rotate it head to foot after a month
    Tip. Put the trial return deadline in your calendar the day it arrives. It is the one thing people forget until it has passed.

If something has gone wrong

It is not expanding to full height

Give it forty-eight hours in a warm room. Cold foam expands slowly, so if it arrived off a cold truck it can take longer. Walking gently on it also helps the cells open.

It smells strongly

That is off-gassing and it is normal and harmless. Leave it bare with a window open and a fan running for a day or two.

I cut into the foam

A shallow nick in the cover is cosmetic and will not affect the mattress. A deep cut into the foam cannot be repaired. Contact the retailer, but be aware opening damage is often excluded.

There is a dip where I sleep after a few months

Check the base before blaming the mattress. Slat gaps wider than about three inches, or a missing center support, will cause exactly this and are usually the real culprit.

Can I put it back in the box to return it?

No. Home compression is not possible. Almost every brand with a sleep trial arranges collection or donation instead — check the policy rather than trying to re-roll it.

Words you will see in the manual

off gassing
The temporary smell from new foam. Harmless, and it fades in a day or two with the window open.
slat
One of the wooden boards that spans a bed frame to support the mattress. Gaps wider than about three inches will make a foam mattress sag.
bunkie board
A thin solid platform that sits on a bed frame to support a foam mattress where the slat gaps are too wide.
law tag
The legal label sewn to a mattress. Photograph it — warranty claims need the model and date from it.

This same guide covers

Memory foam mattresses in a boxHybrid and spring-in-a-box mattressesMattress toppersBunkie boards and foundationsFuton mattresses

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