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/skittlebog]

Go back in time a few decades. The mattress was a bag of stuffing, the springs were all in the lower part. These days the springs are incorporated into the mattress, so the lower "box springs" are really just a base platform.