I have a 3,000 cu. in day-and-a-half Camelbak hunting pack (Commander). It has a black neoprene hose cover and and heavy duty black rubber bite valve cover. The hose is routed into a zippered sleeve on my right shoulder and this does help insulate it also.

Still I had to make a double thickness fleece cover for the last 6" of the hose and mouthpiece to prevent ice buildup, even with blowing the water back up the hose after every drink.

I've put chemical hand warmers in the zippered back compartment where the bladder resides and this has helped a lot. Keeps the water warm and the warm water melts any ice in the hose & bite valve with each drink until temps get into the 10 F. to zero range.

I'm going to try the larger, self-sticking Thermawrap chem heaters that are made for sore muscles. I may even cut one and stick a short piece on the fleece that covers my bite valve.

Eric