Been shopping here for a hybrid mattress a long time, studied the descriptions, read the reviews and took my time. Was a bit nervous about the mattress opening to the full thickness, but went ahead with it and so glad I did! Pics show mattress after 10 minutes. It did thicken later to just about the 10" advertised. Very pleased. As you can see there's no wrinkling or issues with the covering.There was no 'date packed' on mine anywhere, but it said 'open within 72 hours'. Opened mine right away. Beautifully packed, del by UPS, box a bit beat up but all perfect inside, triple wrapped and burst into full size in about 3 minutes. As I'm awaiting delivery of a Zinus wood and metal bed frame, mattress is temporarily on my old bedframe, and an ancient box spring, which will go in the trash. To protect my new mattress I put a sponge topper underneath, you'll see in pics (and not part of new hybrid). To keep the cooling effect I put only a percale sheet on top. On to the comfort, etc. My mattress was old and soft, so this felt a bit firm to me at first, but after only 1 night (got it yesterday) I'd describe it as many have: medium firm. I like it very much as I already woke up w/less aches and pains. And it does have the cooling effect I needed. Looking forward to putting it by itself on my new Zinus frame. It will probably be a little low for me, I'm used to what you see, so I'm planning to get a set of bed risers once I figure out the height I prefer. I'll update all when I get my new frame and get this hybrid on it. Mattress is a great deal with all the desired qualities I wanted at an amazing price.UPDATE: A few weeks later love my new mattress even more!! Haven't slept this well in years. And with my new metal and wood Zinus bed frame (not shown in pics) it's even better. And I do not need bed risers at all! Very pleased.I spent over a year researching bed-in-box mattresses and this was the one I just kept coming back to because of the price for a hybrid King. I wanted a hybrid mattress that was at least 10 inches with a medium-firm feel. This fits the bill.Shipping time was the killer for me. I actually bought this mattress in August and waited two months for it to ship. Then when it finally did another two weeks passed before I had to get on the phone with ...Amazon, the shipping distributor, and then finally the shipping receiver to find my mattress. Apparently it became lost in transit, but I will say, Amazon was quick to replace and scheduled a new one to be delivered by the end of that week. My personal problem was that it was now arriving during a time that my fiancee would be gone for a work trip. I'm only 98 lbs and the box weighs as much as me. I ended up having to leave it in our living room against the wall for 3 weeks until he returned.Now it does say on the side of the box to open within 3 days. I was very nervous about this but my worry for nothing because it opened and expanded perfectly after sitting in a box for 3 weeks. Within 30 minutes it was practically full and we were trying it out. We did not sleep on it the first night but let it get that full 24 hours to expand. There were no odd smells from opening the bed.It's been 2 weeks or so since we started sleeping on this new bed. It is firm. I can feel the first foam layer and it molds to my body only slightly. I honestly don't like firm mattresses ... but my fiancee loves them so he really likes how firm this bed is. With that said I don't mind the firmness and have had some great nights of sleep. You could certainly buy a 2 or 3 inch memory foam cover for this bed and I think that would be good for those who want a little more cushion. Or get the 12 inch. I'm not sure about the cooling feature - haven't noticed anything - so I'll update later on.PROSIf you like firm - this is FIRMExpanded very fastPriceCONSThe box is so heavy - highly recommend getting delivery to room if possibleEdges are not the greatest if you're more than 200 lbsFiber glass (Just don't remove the cover..)1 YEAR UPDATE: Changed from 4 Stars to 5 Stars!!As I mentioned previously, I am not a fan of firm mattresses but I have loved sleeping on this mattress over this past year. I am definitely less sore waking up in the morning. Did not purchase a topper. It has such a nice cushy feel while still being firm. And it has kept that same feeling over the course of daily use this past year.The cooling feature does work! We live in Florida and during the summer we sweat a lot. I noticed a difference right away in that our sheets don't nearly need to be washed as often. We are staying cooler and sweating less. I don't necessarily feel that the mattress is cool but I know that it's keeping our body heat at a cooler temperature.There has been no indents and I haven't felt the need to flip the bed top to bottom. I am very happy with this hybrid mattress. So much so that I remembered to come back and update this review!I bought this for my son and we are both very pleased with this mattress. We opened the box a few days after it arrived and let us expand for 24 hours before putting it on the bedframe. The mattress had expanded cto the full 12 inches by this time. We did leave it for another 12 hours after putting it on the frame before using it. This is a very comfortable mattress and my son has been getting great quality sleep since he's been using it. I like it so much that I'm thinking of getting one for myself!I am 9 months pregnant and my mates just arrived. It was heaven. I finally didn’t wake up sore and hurting to move, I could turn over so easily! I love this mattressThis was my first time purchasing a mattress on amazon. At first I was not so sure if I should buy a mattress without trying it at a store, but it turned out to be great. The mattress is just as firm as I expected and is great for side and back sleep. The cooling feature is also very nice.We bought this for our son for his dorm apartment. It is solid as advertised, and also cooling. When we arrived another boy had the same mattress. Great mattress for a great price.Had major surgery and needed something comfortable. This did the trick. It was inexpensive and easy to "assemble".I was very worried about getting a new mattress because I have back pain and I had learned how to be comfortable in my old bed but I moved across country and couldn’t bring it with me. This bed is AMAZING, it’s quite firm but very soft. My hips don’t hurt after laying on one side for “too” long anymore. I can find a comfortable spot laying on my stomach which I have not been able to do since childhood (I’m a C cup). I honestly love it.Buyer beware, this item was delivered quick and as per instruction to open the package within 72hours and let it expand for 48hours... did all that and the mattress still did not expand to full size, some are 8 inches some areas are 9 and none expanded to full 10 inches.Please note this is a mattress in a box, so once you open it, it will be impossible to repackage by yourself.Called Amazon only to be told that I will need to "purchase a return package at a cost of $99" so I can return the item to amazon and was told by a supervisor to contact zinus instead, only for zinus to say to deal with amazon as its within the 30 day return policy! Called Amazon again and was told nothing they can do unless I pay for a return package! And they will not entertain anymore inquiry regarding this item unless I agree to pay for return packaging! Been a prime member for way too long, never had issues like this. Oh by the way, looks like amazon deleted previous reviews regarding same issue about this mattress.Always been a fan of zinus product but looks like this one is a miss hit.I bought this mattress because it was a good sale, however, I wouldn't hesitate to purchase it again at full price. Great support, firm, but comfy at the same time. Best value I've found in a mattress.