When any of the sorbothane wonder pads get down to +40*F they begin to stiffen up. Once you are at +20*F they are simply a block of plastic. You want something that can actually move like the standard Pachmyer ventilated jobs. Another alternative are the Silvers pads. They are made of rubber and won't stiffen in the cold, but still, the ventilated work best since they actually allow for squishing by about 1/2".
