Maybe the tissue paper thin top layer of this mattress pad is cotton, but the bottom layer is polyester or something synthetic that is NOT breathable. It is like a heat shield redirecting the heat from your body right back up to you - like saran wrap! The rest of my body can be comfortable or even chilly, while the parts touching the mattress become hot and sweaty. I am reviewing this after several nights of lost sleep after which I cannot take it any more and would rather sleep without a mattress pad for the time being than to spend another night on this. Also, the mattress pad looks like it is of nice quality (until you sleep on it) but despite overstock's claim that its retail price is $69, no one would possibly mistake it for that expensive an item! It's laughable, man. Ha!