For the alpinist looking for a lightweight, low bulk bag suitable for cold temperatures, the Neutrino 400 offers exceptional packability and warmth for its weight. Designed with a narrow mummy fit, for reduced bulk and pack size, and constructed with lightweight, high performance materials. It’s perfect for three season mountain missions.    The Neutrino 400 is filled with 400g of 800FP, goose down, stabilised in chevron shaped baffles, cleverly designed to reduce the amount of fabric needed compared to traditional horizontal baffles. The trapezoid boxwall baffle construction allows the down to fully loft, eliminates cold spots, and maximises warmth. Additional baffles along the length of the zip and around the neck decrease heat loss, and with an adjustable drawcord around the hood you can cinch the bag around your face.    Now built with a recycled nylon lining and recycled Pertex Quantum outer, it’s wind resistant and a little lighter on the planet too. The down is also finished with a Nikwax, fluorocarbon-free hydrophobic treatment for coping with condensation. It has a ¾ length zip with anti-snag zip guards, a zipped internal stash pocket and comes with a waterproof roll-top compression sack for easy stashing.    Hand-filled in the UK, all of Rab's down bags benefit from never having had their down compressed before use, maintaining the down’s loft and warmth.