The mattress is solid, supportive, and comfortable EXCEPT that I learned the mattress cover is lined on the inside with FIBERGLASS as an inexpensive ways to meet federal flame retardant regulations. If you unzip the mattress cover (don't!) you will have tiny fibers of glass all over the place and they are very difficult to get rid of. The way these small glass fibers can go everywhere when you open the cover makes it pretty clear they haven't been locked into a gel or something so they can't come out over time (like on a surfboard where they're locked into a resin compound), especially as the outside of the porous cloth mattress cover naturally degrades over time from body heat, perspiration, friction, etc.
BUT...I just can't imagine how it could be healthy or safe to lay sleeping (for years) with thousands of tiny loose glass fibers just millimeters from your nose and mouth. If someone can explain to me why that's not at the very least risky, I'm all ears and open to being wrong. Baring that, I do not understand why Amazon and Zinus would risk selling a sleep product lined with tiny loose glass fibers. Definitely not a gamble I'm going to take with my son's health.
* I gave my review 3 stars because the mattress itself seems good and everything we hoped it would be as a mattress and also so that people will read this review and be able to make their own decision and not just skip it thinking it's some unreasonably irate person who can't believe this $200 mattress isn't as comfy as their $3,000 Tempur-Pedic.