The short answer: It buys you time, but it isn't a heater. Insulation slows down the heat transfer, but the water sitting in the tube will eventually freeze because it has a high surface-area-to-volume ratio. Most experienced cold-weather hikers pair an insulated sleeve with the "blow-back" method, blowing air into the tube after sipping to push the water back into the (warmer) reservoir.

Important Caveat: The Bite Valve

The most vulnerable part of the system is the bite valve. Even if your tube is insulated, the valve is a small, uninsulated piece of silicone exposed to the air. In winter, this is almost always the first part to freeze. A "bite valve cover" which is essential for temperatures below 20 degrees. We recommend adding our Drink Tube Bite Valve Cover.

Absolutely. While most people think of insulation for winter, it's arguably more popular for preventing that "first sip of hot water" during summer hikes. A neoprene sleeve can keep the water in the tube at a drinkable temperature for significantly longer when exposed to direct sunlight.