Bison StormShield -40°C Sleeping Bag

Bison StormShield – Weather-Resistant -40°F Expedition Sleeping Bag.

Whether you’re pushing beyond the Arctic Circle or climbing above 8,000 meters, the Bison StormShield is a weather-resistant -40°F expedition sleeping bag built for the most extreme environments on Earth. When survival depends on your gear, this is the bag you want in your pack—or more accurately, your sled.

Every feature of the Bison is engineered to maximize warmth and retain loft in brutally cold, wet, and windy conditions. The StormShield™ shell fabric is windproof, water-resistant, and highly breathable, protecting the insulation while allowing moisture to escape. Inside, a massive 42 ounces of 850+ fill power goose down is arranged in patented V-Block side baffles and horizontal cross-baffles, locking in an astonishing 10 inches of loft.

Double interlocking draft tubes run the length of the zipper, and an oversized, weather-sealed draft collar encircles the neck to seal in precious body heat. The down-filled hood features a differential cut and a form-fitting shape that insulates without compressing the loft, providing warmth and protection even in spindrift or howling winds.

Despite its expedition-ready design, the Bison remains surprisingly packable for its warmth class. It’s the ultimate choice for polar explorers, winter mountaineers, and high-altitude expeditions where exposure can last for days and shelter is minimal.

Made in the USA with meticulous attention to detail and the highest-quality materials, the Bison StormShield is the warmest sleeping bag Western Mountaineering offers. It’s more than a sleeping bag—it’s a life-support system for the coldest places on the planet.

Features

• Filled with 850+ Fill Power ethically-sourced premium goose down
• V-Block side baffles provides phenomenal down control and improves insulation in colder temperatures
• Weather-resistant StormShield shell protects against extreme wind and moisture, while maximizing inner breathability
• Two Interlocking Draft Tubes seal the sleeping bag against cold wind and help retain inner temperature
• Offset Insulated Double Draft Tubes.
• Durable, abrasion-resistant footbox lining great for storing heavy boots & alpine equipment
• StormShield-Lined insulated external hood ruff seals the bag out from freezing temperatures while retaining internal heat
• Comes with ultralight stuff sack and breathable mesh storage bag
• 4 lbs. 6 oz. Total Weight

Specifications

• Shape: Mummy (w/ full collar)
• Temp Rating: -40°F
• Fill: 850+ Power Goose Down
• Color: Magma
• Country of Origin: USA
• Fabric: StormShield
• Loft: 10.5" in
• Inside Girth (shdr/hip/foot) 
  • 6'0": 64"/55"/39"
  • 6'6": 64"/55"/39"
• Fill Weight
  • 6'0": 42 oz
  • 6'6": 45 oz
• Total Weight
• 6'0": 4 lb 5 oz
• 6'6": 4 lb 9 oz
• Stuff Size
  • 6'0": 11"x22" XXL
  • 6'6": 11"x22" XXL