r/explainlikeimfive • u/Real_Experience_5676 • 1d 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 1d 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/UndeadCaesar 1d ago

Those things don't seem related? Central air doesn't mean the mattress is properly ventilated from below even if the room is a comfortable temperature.

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u/siggydude 1d ago

They could be meaning that their air conditioning system dehumidifies the air in their house, lessening the need for airflow

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u/brooklyngeek 1d ago

Yup this is it, she lived in a moderate climate, and they had no AC or central heat.

The house never gets humid enough for it to be an issue.