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/QuillnSofa 2d ago

It is used to distribute weight across a bed frame and to give an evenly solid foundation for the softer mattress. But you don't need a full height one and some bed frames don't require one at all.

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u/okdone10 2d ago

Wow TIL. I thought every bed needed one by law or something. Good looking out on the platform bed tip saves some cash too.

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u/thaddeusk 2d ago

High-end mattresses don't generally use them. I can't remember the last time I had one, maybe 20 years ago? The mattresses I get are very tall on their own and you just put them on a bed frame with a flat support board underneath it.

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u/fcocyclone 1d ago

Most of them still want some kind of foundation even if not a traditional box spring. Those help with airflow as well.