Just kidding, they were regular mattresses,but the firmest I've ever slept on.
They are so firm that when you sit on them they don't give...at all. You hit the bed like it's a wooden bench.
I have a bad back and I thought that would be a good thing, but the first two mornings I was shaken from my sleep by the ever-growing, excruciating pain in my back.
I had to hobble over and take a hot shower just to get back to semi-normal.
I would suggest an air mattress or some kind of mattress pad if you have back problems like me.
I used a camping-type air mattress that went and bought in Cancun...it made a world of difference.