Rab Mythic Ultra 120 Modular Down Sleeping Bag

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The Rab Mythic Ultra 120 Modular is a lightweight, warmth-efficient sleeping bag that pairs with the Ultrasphere 4.5 pad or other inflatable mattresses. It strategically places insulation where needed, eliminating unnecessary weight.

Rab says: 

Designed as the perfect complement to the new Ultrasphere 4.5 sleep mat, yet versatile enough to be used with other inflatable mats, the award-winning Mythic Ultra 120 Modular cuts weight and bulk by only including insulation where it’s not already provided by your mat. The upper bag, and underside of the legs, is filled with ultra-high-lofting 900FP down and heat-reflective TILT, reducing radiant heat loss without a gram of unnecessary weight. Meanwhile, the lower bag hooks around the mat which insulates you from the ground.

The result is an ultralight bag that, when combined with the Ultrasphere 4.5, forms a sleep system that weighs under 700g yet allows you to sleep comfortably down to 0°C. With a tiny pack size and uncompromised comfort, it’s the perfect sleeping bag for long-distance trekking, bikepacking, and multi-day mountain runs.

The lightweight stitch-through construction is low-bulk, with the down strategically positioned to optimise warmth. Secure the bag onto your sleep mat using the back harness, while the insulated side baffles marry up to the side of the mat to keep cold spots at bay. We’ve chosen a diagonal zip to allow easy entry and exit, as well as plenty of ventilation on warmer summer nights. Stash clothing in the hood sleeve to create an ultralight pillow, further streamlining your kit list.

The Mythic Ultra 120 Modular is hand-filled in the UK to ensure that its down has never been compressed before use, retaining its loft for your first epic adventure.

Our Verdict

The Rab Mythic Ultra 120 Modular is an innovative ultralight sleeping bag designed specifically to pair with Rab’s Ultrasphere 4.5 sleeping pad. However, it can be used with other inflatable mattresses as well. At just 345g for the bag alone, it achieves an impressive warmth-to-weight ratio by strategically placing 900 fill power ethically sourced hydrophobic down insulation where you need it most.

The upper body section and underside of the legs are insulated, while the back section has no insulation since your sleeping pad will provide that warmth. This eliminates unnecessary weight and bulk. Combined with the Ultrasphere 4.5 pad (rated to 0°C), the sleep system weighs under 700g yet keeps you comfortable with freezing temperatures.

The bag comes with a sleeve designed to accommodate the Ultrasphere sleeping pad. While most regular-sized pads may fit, wider, longer, or shorter pads may not.  An elasticated fastening system to secure the pad would have addressed this issue but it is lacking.

The 10D recycled shell fabric is treated with a fluorocarbon-free DWR, and the foot box utilises Rab’s heat-reflective TILT lining to boost warmth further. With a tiny compressed size, premium materials, and intelligent insulation mapping, the Mythic Ultra 120 Modular is an outstanding option for ounce counters looking to cut weight without sacrificing warmth on multi-day treks, bikepacking trips, or fast-packing missions.

– Reviewed by Ultralight Outdoor Gear

Features

• Rab sleep limit of 0°C (32°F) achieved with air mats rating R4 or above
• 10D Recycled Atmos™ (27gsm) with Fluorocarbon-Free DWR
• 10D Recycled Atmos™ (28gsm) with Thermo Ionic Lining Technology (TILT)
• 900FP European Goose Down with Nikwax Fluorocarbon-Free Hydrophobic Finish (120g/4.2oz)
• TILT and 900FP down on upper bag and lower legs achieves high warmth to weight ratio
• Integrated mat sleeve secures uninsulated area of the bag to air mat
• Rab sleep limit of 0°C (32°F) achieved with air mats rating R4 or above
• diagonal zip entry with YKK® 2-way zip allows easy entry and exit, and versatile venting
• Pillow sleeve designed for folded clothing for use as a ultralight pillow
• Down-filled anti-snag zip baffle
• Lightweight roll-top compression sack included
• Filled in Derbyshire UK
• Optimally filled, lightweight stitch-through construction

Specifications

• Weight: 345g
• Packed size: 16x30cm

Material & Construction

• Main: 100% Recycled Polyamide. Lining: 100% Recycled Polyamide with Metal coating

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