Mythic 400 Down Sleeping Bag

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UOG TOP PICK—Ultra-lightweight with a highly tapered cut, the Mythic 400 is designed for alpine-style missions where weight and pack size are crucial to success. It’s a high-performance bag for those meticulously counting grams, filled with 900FP goose down and covered with a lightweight recycled Atmos fabric.

Rab says: 

The Mythic range is all about slashing weight wherever possible. The Mythic 400 is an extremely lightweight three-season bag. At home in high mountains, it’s ideal for venturing out long Alpine routes, multi-day climbs, treks, or bikepacking adventures.

Weighing in at just 700g, it contains 400g of 900FP goose down. The chevron style baffle design keeps the down in position, optimising core warmth and reducing the amount of fabric needed compared to traditional horizontal baffles. The outer is made from our own wind- and water-resistant, recycled Atmos™ fabric. The bag has a narrow mummy shape to minimise bulk, lightweight zips and pullers, and comes with a lightweight, waterproof, roll-top compression sack for protection from the elements and a small pack size while on the move.

The trapezoid boxwall baffle construction allows the down to fully loft, eliminates cold spots, and maximises warmth. It has an additional, adjustable baffle around the neck and an internal baffle along the length of the zip, both designed stop the heat from escaping. Hand-filled in the UK, all our down bags benefit from never having had their down compressed before use, maintaining the down’s loft and warmth.

Our Verdict

The Rab Mythic 400 Down Sleeping Bag is fantastic for those seeking an ultralight, three-season sleeping bag. Weighing just 700 grams and packed with 400 grams of 900FP goose down, it offers an exceptional warmth-to-weight ratio. The recycled Atmos™ fabric shell is wind- and water-resistant, ensuring reliable performance in harsh mountain conditions. The chevron baffle design optimises core warmth and reduces fabric bulk, making it a top choice for weight-conscious adventurers.

The bag’s narrow mummy shape, adjustable neck baffle, and internal zip baffle minimise heat loss, providing a cosy night’s sleep even in colder temperatures. The trapezoid box-wall construction maximises loft and eliminates cold spots, enhancing overall warmth. The lightweight, waterproof roll-top compression sack ensures compact packing, making the Mythic 400 ideal for long alpine routes, multi-day climbs, and bikepacking adventures.

– Reviewed by Ultralight Outdoor Gear

Features

• Weight saving chevron baffle design, reduces down migration and optimises core warmth.
• Trapezoidal boxwall construction with differential cut, to maximise loft and warmth
• Close fitting adjustable neck baffle design for decreased heat loss
• YKK® 3/4 length main zip with synthetic filled baffle to trap warmth
• YKK® zipped internal stash pocket
• Angled foot box for relaxed sleeping posture
• Anti-snag bonded zip guard
• Lightweight waterproof roll-top compression sack included

Specifications

• Regular weight: 726g (excluding storage bags)
• Rab Sleep Limit: -6°C (20°F)
• ISO EN: Comfort: -1°C (30°F), Limit: -6°C (21°F), Extreme: -24°C (-11°F)
• Sleeping Bag Length: (reg) 215cm / 84.6in
• Max User Height: (reg) 185cm / 72.8in
• Internal Shoulder Girth: (reg) 160cm / 63.0in
• Internal Hip Girth: (reg) 134cm / 52.8in
• Internal Foot Girth: (reg) 102cm / 40.2in
• Packed size: (Reg) 35 x 23cm / 13.8 x 9.1in

Material & Construction

• 10D Recycled Atmos™ (27gsm) with Fluorocarbon-Free DWR
• Lining: 10D Recycled Atmos™ (27gsm) with Fluorocarbon-Free DWR
• 900FP European Goose Down with Nikwax Fluorocarbon-Free Hydrophobic Finish (400g / 14.1oz)

Help & advice:

• The Ultimate Guide to Lightweight Sleeping Bags
• Time-Saver Guide to Choosing a Sleeping Bag
• About Rab
• Rab Mythic Sleeping Bag Range Explained
• Rab Sustainability and Responsibility
• Down Quality
• All About Down
• Hydrophobic Down
• Recycled Content in Outdoor Gear