Ok I am by no means a bedding expert. I own SCSS but I have a regular mattress. Personally at night I sweat like a fatman in august. Wait, I am a fat man and it is august. Moisture seaps into the mattress and gets trapped. (which has now made me paranoid that i'm going to get mold in my mattress, but at least I know in advance).
What I don't understand is how a sheat of plastic and air is going to be any more susceptible to this problem than foam or cloth, which would have gobs of surface area for mold to latch onto and for moisture to be retained. I would think quite the opposite to be true.