Perfect firmness and doesn't get hot at all. I'm so impressed with the quality of this mattress and the comfort.
I live in the dessert and I have constant back pain from scoliosis. I was worried a memory foam mattress might not be the perfect fit, because I heard they soak up body heat, get hot and also how they loose their firmness. Those are total non factors with this bed. The mattress is so well made it stays cool and doesn't heat up. The bed is firm and supportive, yet soft and plush at the same time. It actually helps me with my back pain and I'm just as comfortable sleeping on my back as I am on my sides. Something I could never really do before. We've had it for 2 months, no signs of any lumps forming, its just as perfectly flat as the day we got it. We sleep great!