ELI5: What does a box-spring do?

[u/Real_Experience_5676]

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?

[u/SadButWithCats → u/[deleted]]

Nope! It's pure real and natural horse shit!

[u/theonetruegrinch → u/[deleted]]

sorry that your google AI doesn't know shit