What I learned (the level-headed part)

I purchased a queen-sized Casper Dream, and deeply regret my purchase. The poor out-of-the-box smell of their mattress is well documented on this sub [1] [2] [3] [4], but I wanted to add a point I unfortunately didn't consider or give credence to before buying. I wish I noticed that many mixed reviews (such as post [4] above) were able to escape their apartment for a week or two when the mattress smells the worst, and usually still note that the mattress smelled bad afterwards. If you (like me) work from home and/or live in a small apartment, you do not get to escape the mattress at its worst and will be exposed to this mattress for extended periods of time (which other reviewers may not have experienced) which, in my experience, led to the adverse effects of the smell compounding.

Be prepared to order this mattress, spend 3 days to a week to discover both you cannot put up with the mattress smell and that there's no sign of it going away. Then, when you request a return, expect to have to hold onto the mattress for up to 30 days waiting for the Casper reps to remove it from your residence, meaning you will still be without a bed but still have to put up with the smell. Chose for yourself if this is worth your time and money to roll the dice on if you get to pay over a thousand dollars to make your apartment or bedroom unusable for up to 30 days.

My full story (the emotionally-charged part)

First of all, be extremely skeptical of any review that claims to have slept well on the first night, as Casper recommends you air the mattress out for multiple days. I put far too much belief into external reviews or accounts of the smell going away after a couple of days, or thought the smell just wouldn't be that bad and that I would be able to ignore it. It is worth noting that I submitted a review for the mattress on their website. When you submit, it says your review may appear on their website, not that it will appear. At the time of posting, my review has not appeared, so be skeptical that their 4.6 rating is them cherry picking reviews that are favorable to them!

My apartment is genuinely unusable so long as this mattress is in my bed room, as I get a debilitating headache no matter where I am in the apartment. I can taste the smell everywhere I go, and it takes about an hour of being outside for me to get my wits back. Note: it is not a standard rotten smell that you can just ignore, it smells like you are continuously inhaling chemicals. I evidently don't get poor air circulation trapping the gasses in my bedroom that just need to be aired out as the smell circulates to my entire apartment, the mattress is just continuously off gassing. I cannot review the comfort of sleeping on the mattress as I cannot go near it for any longer than 10 minutes. Even when I spend over an hour in my apartment and adjust to the smell itself, my headache, lightheartedness, and nausea persist.

Call a Casper representative and they tell you the smell can last up to two weeks, and that they'd be happy to offer an exchange, but it's evident from other reviews that the smell can go on for far longer. Also, why would I want to exchange, only to have to wait another two weeks to see if the replacement has the same issue? General unawareness from their representatives on how this can actually ruin your life for the better part of a month. Assess for yourself if it's worth waiting two weeks with a horrid smelling mattress to see whether or not the smell dissipates. Do not get this mattress unless you don't need it immediately *and* have a garage or something to air it out in. Not fit for shipping to a smaller space or apartment, or for people who work from home and can't avoid the mattress while it "airs out".