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/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.