Hey Les,
I’m copy and pasting this from another post (I would link but there’s other stuff there–and this is more pertinent).
With hot sleeping, weirdly it’s not about cooling—it’s about humidity control. This has to do with a fibers ability to absorb and dissipate moisture, and well as airflow through the entire structure.
People who live in humid places understand that it’s not the temp that gets you it’s the heat-index which is how hot it feels based on how damp the air is. Basically, 90 degrees and dry, with a little breeze is way more comfortable than 80 and humid with no air movement.
Many mattresses marketed as “cooling” use gels, synthetic foams, or phase change fabrics that may feel cool at first but trap heat and moisture over time, making you feel clammy, which in turn makes you feel hot.
A better approach is choosing breathable, moisture-wicking materials that let air and moisture move freely (think: convection). Talalay latex has excellent airflow (dunlop is good as well, albeit to a slightly lesser degree), while cotton and wool help regulate temperature by keeping you dry, and helping to regulate humidity.
Side note: All foams, even latex, can be sweaty. This is why you want to have them covered with cotton and wool. This creates a layer that can absorb liquid perspiration (the cotton), and vapor (the wool), helping keep you dry. The airflow through the coils and latex is keeping those layers dry.
If possible, avoid waterproof encasements, or allergy covers, as they can trap humidity by the sleeper and make overheating worse. (Mattress pads with polyester fill can make you sweaty too.)
Also, your bedding plays a huge role—skip down or polyester comforters and opt for lightweight wool or cotton instead. Stick to 100% cotton or linen sheets, which allow for better airflow and moisture dissipation, helping you stay drier and more comfortable throughout the night.
Regardless of materials, softer mattresses are also always a bit warmer than firmer beds (just because more of your body is in the bed), and “hybrids” tend to have better airflow and moisture reduction than solid foams.
Lastly, even though they are marketed as “cooling”, I have never felt that bamboo, rayon, tencel, lyocell, or other cellulose product, or silk, are any better than a poly blend for keeping you feeling dry. There may be other opinions on this and sometimes you just have to try it out and see. If you ask me (which you didn’t lol), I would stick to cotton and wool.
