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A very warm, reliable down sleeping bag designed for winter and extreme cold conditions
Rab says:
Warm, robust, and reliable down-filled sleeping bag for regular mountain use. Built to prioritise comfort with a wide mummy shape, roomy footbox, and sidewall baffles, it's perfect for trekking and backpacking adventures.
Our Verdict
The Ascent -18C uses 650-fill-power duck down with a substantial 880g fill to deliver serious insulation, weighing 1267g. This level of fill prioritises dependable warmth over minimising weight, providing a stable warmth-to-weight ratio for deep winter use and colder mountain conditions. The comfort limit of around -18°C feels realistic when paired with an appropriate mat, offering high protection in consistently cold environments.
The wide mummy cut remains a defining feature, offering noticeably more space than most performance-focused bags and allowing easier movement in the bag at night. The L.O.F.T construction uses alternating baffle sizes to distribute down more efficiently, helping maintain warmth without unnecessary bulk. Sidewall baffles keep the insulation positioned around the body, reducing cold spots and maintaining loft when moving. A 3/4-length two-way zip and an additional arm zip help manage ventilation and tailor the level of insulation.
The Pertex Quantum fabric balances weight and durability, and the overall construction feels robust for a bag designed for colder use. Features such as the insulated collar, shaped hood and internal pocket support comfort in camp. Overall, this is a well-balanced option for those prioritising warmth, comfort and reliability in a capable cold-weather sleep system.
- Reviewed by Ultralight Outdoor Gear
Features
- L.O.F.T™ baffle technology reduces down migration, optimising heat retention and pack size
- Sidewall baffle construction for increased down loft and greater side sleeping comfort
- Anatomically fitted hood with drawcord adjustment to maximise comfort and heat retention
- Internal cordlocks positioned below the collar bone for greater side sleeping comfort
- YKK® zipped internal stash pocket
- 3D shaped neck collar with recycled Stratus™ insulation
- 2-way YKK® 3/4 length main zip with synthetic-filled baffle
- YKK® anti-snag zip insert and anti-snag internal zip guard
- Anatomically shaped foot box for relaxed sleeping posture
- Drawcord stuff sack included
- Zipped storage sack with water-resistant base for home storage
- Hand-filled in Derbyshire UK
- Wide mummy shape
- YKK® zipped arm access vent with integrated snap closure to retain heat during tent-based tasks
- Temperature rated in accordance with ISO 23537-2:2022
Specifications
Temperature Rating
- Comfort: -10°C
- Comfort Limit: -18°C
- Extreme: -40°C
Regular
- Weight: 1267g
- Lenth: 215cm
- Width: 80cm
Long
- Weight: 1302g
- Lenth: 230cm
- Width: 80cm
Material & Construction
- 20D Pertex® Quantum nylon ripstop (38g/m²) with fluorocarbon-free DWR
- Lining: Recycled 20D nylon, 38g/m²
- 650FP European duck down with Grangers fluorocarbon-free hydrophobic finish (880g / 31.0oz)
- 100% Woven Polyamide Shell , Down filled sleeping bag
