It does expand to a full 12" like promised. Like other reviews the bottom corners have stayed crushed but they don't effect the mattress performance or appearance at all. This mattress is hard! The top foam layer is not soft enough to take pressure off of your pressure points such as your hips and shoulders. It sleeps cool but I wake up with a sore body every day from its use. I was going to scrap it until just one week ago (Dec. 2018) my wife and I put our 3" gel foam mattress topper from our RV on the bed. Whole world of different sleep comfort. We'll see how it goes, we have until Spring to pull the RV out again, and if it continues to offer good restful sleep we'll but another topper for the RV.
"Our mattresses typically take 48-72 hours to decompress, but it can take up to one week to fully decompress in some cases. You can sleep on the mattress during this time, sleeping on the mattress will not slow down the decompression process. Please let us know if the condition of your mattress doesn't improve and we would be glad to send you a replacement under warranty.
Please contact us by submitting a ticket at support.zinus.com or call us at (800) 613-1225 -Zinus"