After struggling through a recent sleep-killing heatwave, I've finally managed to get my hands on the CoolNest Memory Foam Mattress, now $399.99 (was $699.99) at SweetNight in the 4th of July sales. The CoolNest Mattress is designed to add cooling comfort to your sleep set-up — but does it deliver on its promise?The best mattresses on the market typically have some degree of cooling features, as overheating stops you from falling asleep. The CoolNest takes things up a level. A dedicated cooling model, it uses an airflow-boosting cooling cover and heat-dissipating Phase Change Material (PCM) to guarantee a bed that's 8°F cooler than standard memory foam mattresses.But as mattresses don't always live up to their hefty promises, I decided to give the SweetNight CoolNest Mattress a try ahead of the 4th of July mattress sales (and another heatwave). While a full review is coming soon, here is my first impression of the SweetNight CoolNest Mattress.Easy to set up Image 1 of 3(Image credit: Future)Like the best mattresses in a box, the CoolNest is shipped compressed, rolled up, and wrapped in plastic. This shipping method means the CoolNest needs to be unboxed, unwrapped, and left to expand.I unboxed the CoolNest with a fellow mattress tester (unboxing a mattress tends to be a two-person job) and we were pleasantly surprised how easy it was to set up. We had previously unboxed a bulky hybrid mattress, so the all-foam CoolNest was a dream in comparison. There was minimal off-gassing, too.As for the expansion time, there's little to worry about — it was ready in hours. Fresh from the box it did look slightly squished (especially at the corners) and I worried we'd be waiting a while to test it. Plus, SweetNight writes on their website that it takes its mattresses 72 hours to fully expand.However, the CoolNest Mattress seemed to plump up to its full size within hours of unboxing, and the brand says their beds are safe to sleep on within 6 hours of opening.Get instant access to breaking news, the hottest reviews, great deals and helpful tips.