Alpine Down Mountaineering Sleeping Bag -40 °c - Sea To Summit UK

Alpine ApIII -40°c

Our first choice for extreme cold and high altitude conditions where sleeping well can make or break an expedition

From £730.00

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Insulation Type
RDS 90/10 Premium Goose Down
Nano Shell
Fill Power
ULTRA-DRY Down® 850+ Loft
Fill Weight
Regular: 1250g, Long: 1440g
Contoured Mummy
Temp Rating
EN -29°c Comfort to -40°c Lower
Regular: 1870g, Long: 2100g
Selling Price

Our Alpine™ Series combines our most technical sleeping bag features to deliver reliable performance while cocooning you in the highest quality RDS 850+ Loft Goose ULTRA-DRY Down™.

Designed for high altitude mountaineering and arctic conditions, the contoured mummy design delivers efficient insulation, while our updated expedition sizing provides space for extra clothing to be worn inside the bag. The anatomically shaped and oversized footbox can comfortably accommodate boots when necessary.

Vertical baffles over the chest section ensure the down insulation cannot migrate or shift to the outside of the bag during sleep, creating cold spots. A side block baffle construction maintains the 60/40 fill ratio, keeping more down on the top of the bag for maximum insulation.

Our ULTRA-DRY Down™ water-repellent treatment protects the down from external moisture and condensation from the inside of the bag, virtually eliminating the negative effects moisture has on down. All Sea to Summit Down Sleeping Bags use Responsible Down Standard (RDS) certified down.

The Free-Flow Zip system provides a half zip on the right side of the bag to provide freedom of movement for both arms as well as additional ventilation. The full length, two-way left side zip provides easy access and extra ventilation options.

Our waterproof yet breathable NanoShell™ fabric provides protection from wind and moisture. The tightly sized and carefully panelled hood fits snugly around your head, allowing you to maintain maximum warmth with minimal adjustment.

An oversized zipper draft tube is fitted with the lightest and stiffest anti-snag materials for effortless operation and to prevent heat loss through the zipper.

  • Designed for extreme cold and high-altitude conditions
  • Contoured mummy shape for efficient insulation
  • Expedition sizing for extra space and layered clothing
  • Vertical chest baffles prevent down migration and cold spots
  • Side block baffle with 60/40 fill ratio keeps more down on the top of the bag for maximum insulation
  • Anatomically shaped and oversized footbox can accommodate boots
  • Free-Flow half right-side zip for freedom of movement and additional ventilation
  • RDS 850+ Loft Premium Goose ULTRA-DRY Down™ for maximum insulation value
  • Our waterproof/breathable NanoShell™ fabric protects against wind and moisture
  • Snug panelled hood maintains maximum warmth with minimal adjustment
  • Oversized draft tube with anti-snag materials, prevents heat loss through zipper
  • Oversized neck draft tube with a dual adjustment system for even cinching and maximum warmth
  • YKK #5 side zip has two sliders for easy access and extra ventilation
  • Large internal security pocket
  • Includes lightweight Ultra-Sil™ compression bag for compact storage
  • NOTE: This bag is not designed to pair with another


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