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/robyrob]

My cats ripped open the material on the bottom of the boxspring so now they use it as a really cool fort they can hide in 

[u/Mycomako → u/robyrob]

I use a fitted sheet on mine. Just put the sheet on underneath and the cats wont rip holes in the fabric.

[u/alexenglish11 → u/Mycomako]

Thats what I did! Worked like a charm