Hi Pamela -- Thanks for your question. The answer to this can vary based on which mattress model you choose.

Some manufacturers require that their mattress be used on a foundation meeting specific criteria in order for the warranty to remain valid. It's worth noting that this is increasingly rare these days, as most mattresses are designed to be used without a foundation (and most foundations are little more than basic wood boxes that do nothing more than increase the height of your mattress).

That said, all manufacturers require that, at a minimum, their mattress must have solid, stable, study support underneath it. This could include a box spring or other foundation, a slatted base that within 3" or less of each other, a solid platform, or even the floor. The other key is that if you are using a queen or king size mattress, you must have support that run under the center of the mattress and goes all the way to the floor -- it's not enough to have legs on the corners or sides of the mattress only. These requirements would apply even if the manufacturer doesn't require that a certain kind or brand of foundation must be used.

I hope that's helpful.