My bed is already high so I didn’t want to add many inches.  I chose this two inch topper to give a little more “Cush” to my existing mattresses.  Instructions tell us to open and leave out for 24-48 hours and I left both my king and cal king toppers “air out” for 36 plus hours.  I may be overly sensitive to odors,  but I felt it needed the 36 hours of airing out with windows open and an active cross breeze.   Both the king and cal king fit the respective mattresses perfectly, my mattress pad secured them and they add a perfect softness I needed.      I don’t smell any residual odor and I’m quite happy!