I NEVER get warm on this mattress. No even in the midst of Summer. I DO remember 'overheating' the (very) few times I've ever slept on memory foam (at a friends house) and I found it to be very uncomfortable.

The Winx system isn't a necessity, but it helps a lot if you've got back problems (which my wife has). Apart from that, it's mostly the mattress which does the work. It's a very 'breathing' fabric and I never even sweat in my bed. (at least not up to a level that I notice it or it's uncomfortable)