I have a Ridgerest and it's warmer than flat CCF pads because the ridges and valleys create more thickness and more comfort. The little valleys under your bag becone "heat traps" compared to a flat mattress.

Usually winter campers use TWO mattresses, laugh a Ridgerest or Z Rest beneath their regular Thermarest.

Eric
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"There are no comfortable backpacks. Some are just less uncomfortable than others."