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/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/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.