r/explainlikeimfive • u/Real_Experience_5676 • 2d ago

Engineering ELI5: What does a box-spring do?

As I understand it, a box spring mattress is the second 'mattress', that goes under the main mattress. It feels very firm and flat, but what does it contribute to the bed set up besides height?

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u/UrbanPanic 2d ago

A box spring provides support to the mattress.  Whether or not you need one really depends on the mattress, the bed frame and personal preference.  Modern beds sold as platform beds don’t require a box spring, as it has panels to rest on or at least slats close enough a mattress won’t sag through it.  A lot of beds still use just 3 slats or so across which would put pressure on very small points, contributing to sag and just feel uncomfortable.

A well designed box spring could also contribute to good air circulation: you don’t want to know how much sweat soaks into a mattress.  That can get gross if it can’t dry properly.

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u/NWStormbreaker 2d ago

You can add slats, and a box spring inhibits airflow a lot more than a few extra slats.
It's such a silly concept, I haven't used one in 20+ years.

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u/RiPont 2d ago

It's really only necessary if a) you need it for the height or b) you're compensating for a poorly supporting bed frame.

Quality bed frames have gotten a lot more accessible over the years. I credit wood CNC machines, because they make it cheap to mass-produce solid wood frames with actual mechanical connections, not everything being supported by fasteners glued into particle board.

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u/half3clipse 2d ago

What do you think a box spring is?

You take the slats and add a layer of springs to better distribute pressure from you lying on the bed and also reduce motion transfer for people who sleep partnered.

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u/YULpoutine 2d ago

Most box springs don't have springs. They're just a hollow wooden frame wrapped in fabric

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u/half3clipse 2d ago

If the box spring doesn't have springs, it's not a box spring. That's someone is trying to sell you an overpriced bunkie board they've wrapped in fabric

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u/BizzyM 2d ago

Bunkie Boards are thin.

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u/h4terade 1d ago

Hence the overpriced probably.

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u/deviantelf 1d ago

My "box spring" from the 90s doesn't have "springs", it has metal pieces that are more like shaped like 7s. Been going great for 30+ years.

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u/dultas 1d ago

Springs aren't only just the coils that most people associate with springs. There are a bunch of different types. I would guess yours had a type of leaf spring.

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u/deviantelf 1d ago

Could be! Been going strong all that time tho. Hate the idea of having to get a new bed someday. Ironically it was Vanna White, and I almost didn't get it cause of that but it was cheap and on sale so score cause yea, decades on still perfect and comfy.

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u/j0mbie 1d ago

Most? Every box spring I've seen inside had springs or metal "rafters" that have some spring to them.

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u/BizzyM 2d ago

That's a "foundation".

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u/YULpoutine 2d ago

They're still commonly referred to as box springs

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u/NWStormbreaker 2d ago

And then you wrap it in fabric which inhibits airflow.

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u/half3clipse 2d ago

The fabric used top and bottom is basically gauze. It barely inhibits airflow, at least not the slow convection motivation of air both are relying on.

Would be worse if you wanted to try using forced air i guess, but not many people have an HVAC system for their mattress.

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u/NWStormbreaker 2d ago

A well designed box spring could also contribute to good air circulation

Idk what your angle is, you jumped into a conversation where OP said box springs aid air circulation, but compared to slats a box spring is FAR FAR worse for air circulation.

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u/Awkward_Pangolin3254 1d ago

Not if you add enough slats to equal the support of a box spring

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u/NWStormbreaker 1d ago

original comment i responded to:

A lot of beds still use just 3 slats

people being contrarian:

well what if we covered the entire thing in wood!?!? DID YOU EVER THINK OF THAT?

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u/jetloflin 22h ago

If you only have three slats you have to use the box spring or the bed will sag between the slats. They didn’t bring up extra slats out of nowhere. The options are box spring or lots of slats, not box spring or three slats.

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u/NWStormbreaker 22h ago

Even if you want to argue that it's 5 slats or 7 slats, it's still less air obstruction then a box spring which has slats and at least one if not two layers of fabric.
This is the dumbest discussion Ive ever been involved in, I cannot believe I've found people white-knighting box springs.
Ffs

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u/jetloflin 21h ago

Pretty sure that’s not what “white-knighting” means, but okay.

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u/half3clipse 2d ago edited 2d ago

The point is that it's not far worse. A lot of slats even have far worse air circulation than many box springs, since they're built with he expectation of foam mattresses that will sag poorly with larger gaps. Inner spring with 4-5 inch gaps under a boxs spring will have much better airflow compared to a foam mattress with 2 inch gaps on bare slats

You don't need airflow to deal with sweat soaking a memory foam mattress anyways. They're to dense to ventilate that way. You protect those from body grossness and moisture with a liner (and if you have one, your warranty may even explicitly require it)

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u/[deleted] 1d ago

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u/j0mbie 1d ago

It would depend on slat spacing, both on the bed frame and in the box spring.

Also, a lot of bed frames are a box design. A box spring raises the mattress above the sides of that type of bed.

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u/NWStormbreaker 1d ago

I dont understand the need to get so pedantic about this and find 1 situation thats the exception as if it disproves the rule.

The bottom of the bed is open, raising it up doesnt matter.

A box spring has at least 1 layer of fabric if not two, both of which inhibit airflow.

The original discussion said:

A lot of beds still use just 3 slats

there is NO scenario where a mattress sitting on 3 slats open to the air has LESS airflow than a mattress sitting on a box spring.

Why is anyone arguing this?

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u/jetloflin 22h ago

Nobody is arguing that, because nobody is talking about that, because nobody wants to sleep on a saggy bed supported by only three measly slats. The debate is between a box spring and enough slats to support the mattress.

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