Forty Below Bottle Boot 1L

The Forty Below Bottle Boot 1L is a neoprene sleeve sized for 1-litre wide-mouth bottles, adding 126 g to slow down freezing when temperatures drop below zero. The neoprene traps a layer of air around the bottle rather than actively heating it, so it buys time rather than preventing freezing outright on a genuinely cold night — pairing it with an insulated pouch inside your sleeping bag or storing the bottle upside down still helps. The clamshell opening has no zipper to fumble with cold fingers or ice up, which matters when you need quick access at a break. It fits wide-mouth bottles specifically; narrow-neck bottles won't seat properly in the sleeve. Useful for winter camping and shoulder-season trips where nighttime temperatures dip below freezing — unnecessary weight for three-season use where bottles don't freeze.