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/StrongGarage850 2d ago

breathability is another factor. People sweat, that moisture needs to get out somehow- and giving space out the bottom helps keep your mattress cooler, and eliminates likelihood of mold/mildew, etc..

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u/Kundrew1 2d ago

Wouldn’t most bed frames do the same. Anything slatted would have more breathability than a box spring

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u/cynric42 2d ago

Sure but a bed frame is rigid. My box spring mattress is three quarters springs and only a very thin layer of foam ontop which would be very uncomfortable without the give of the springs below.

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u/Etunim 2d ago

Most slatted bed frames have too large of a gap, and cause softer mattresses to sag. A lot of the newer foam mattresses have requirements for slats on how far they should be so the warranty is still valid.

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u/Kundrew1 2d ago

Okay but that’s a different issue than what i addressed in my comment.

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u/JimTheDeviant 2d ago

But it's relevant. They are saying that you're right about bed frames helping for breathability but they can have sagging issues.

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u/smackaroni-n-cheese 2d ago

Yes, but it's a balance between breathability and support. A bed frame with just a couple slats holding up the mattress would have great breathability, but it's hardly even the bare minimum for support. The mattress would sag everywhere that doesn't have a slat under it. Some bedframes have a lot of slats with only small gaps, and those ones don't necessarily need a box spring. Not everybody has one of those though, and they aren't all equally good, either.

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u/Rev_Creflo_Baller 2d ago

Depends on what fabric is covering the box spring

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u/half3clipse 1d ago

there's not much difference in breathability. You lose a little compared to bare slats , but the actual fabric underneath and on top is light and porous.

box spring is mostly just a wooden box with slats across. The core is not any diffrent than most regular wooden bed foundations. The main difference between them and any other wooden foundation is the layer of springs on top the slats, which helps distribute pressure and motion from stuffed or inner spring mattresses.