Super cushy but not too soft & it’s thicker than 4”, closer to 5”.  Our mattress is firm and about 2 years old- good for my back but hard on my hips and side (I’m mostly a side sleeper). Now with the topper both my back and my hips are comfortable and I sleep better- and no morning back pain. It sleeps a tiny bit hot, but nothing unmanageable. We’ve been using it about a week. It has a bit of a smell but we let it air out uncovered with the windows open for a couple days. With the mattress pad and the extra protector we purchased  on top, the smell is now minimal and I’m pretty sensitive to smells. All in all I’m super happy with it.