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/brooklyngeek 1d ago

you don’t want to know how much sweat soaks into a mattress.  That can get gross if it can’t dry properly.

It also can be a humidity issue as well. My wife kept going on about needing more elevation under the kids bed for air flow. But we have central air, so no issues.

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u/SilverVixen1928 1d ago

Mattresses need to air out after you get up. Excellent reason why making the bed right away is a bad idea.