As soon as this mattress was unwrapped it popped up to 14 inches, it was quick and immediate. It was like it was waiting to be released. They don't recommend sleeping on it the first night, but I was so exhausted, and it appeared at maximum height, felt so smooth and cool to the touch, I went for it and slept well.  I typically have 12 inches with mattress and boxspring, but I purchased an adjustable frame and the mattress alone did not sleep well. 14" does require a bit more effort to get in; due to my height, I can't readily sit on the bed from a standing position but can lower the bed frame legs. I have a little step stool should I ever need it. The mattress is a bit softer than expected but very comfortable. I am not sure if it being less firm than expected is due to not allowing time for full expansion before I slept in it but so far, I am pleased.