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Rab Mythic 400 Review

A premium bag that's designed to minimize weight and packed size
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rab mythic 400 backpacking sleeping bag review
Credit: Rab
Price:  $600 List
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Manufacturer:   Rab
By Jack Cramer ⋅ Review Editor  ⋅  May 7, 2019
  • Warmth - 20% 7.0
  • Weight - 20% 9.0
  • Comfort - 20% 5.0
  • Packed Size - 15% 8.0
  • Versatility - 15% 4.0
  • Features & Design - 10% 5.0

Our Verdict

At first glance the Mythic is an incredible sleeping bag. Rab combines premium 900-fill power down, silky Pertex Quantum fabric, and a minimalist zipper to create a bag that's plenty warm yet also ultralight. But when you step back and compare it with other ultra-premium bags, it doesn't look quite as good. Under closer inspection, the tiny zipper saves weight but is prone to snagging. Moreover, the short zipper length limits your ability to vent excess heat on warmer nights. Its spartan dimensions also contribute to its low weight but can be uncomfortably constrictive for larger folks or side sleepers. Ultimately, the Mythic is still an awesome bag.
Lofty 900FP down
Packs small
Solid warmth
Waterproof stuff sack
Short half-length zipper that's prone to snagging
Narrow leg dimensions
One size "fits" all

Our Analysis and Test Results

When comparing the Mythic 400 with its competitors in the backpacking sleeping bag review, it's essential to factor in that the Mythic we tested was a size regular while all the other bags were size long. This does make the comparison more difficult, but it was our only option because the Mythic only comes in one size. Fortunately, a Rab size regular was just long enough for our 6'2" lead tester. Anyone 6'3" or taller, however, will likely be happier in a different bag.

Performance Comparison

rab mythic 400 backpacking sleeping bag review - if the rab mythic makes so many sacrifices to be ultralight, may be...
If the Rab Mythic makes so many sacrifices to be ultralight, may be you should to. Pair it with an ultralight shelter, or no shelter at all, and it's possible to cover serious mileage.
Credit: Jack Cramer


To keep you cozy the Mythic 400 is filled with 14.1 ounces of premium 900 fill power goose down. It also features a small neck baffle and half-length zipper to seal the heat in. With this insulation and features, it receives an EN lower limit temperature rating of 21°F. Our testers feel this rating is accurate compared to other EN-rated bags.


The Mythic 400 is optimized for minimum weight. To accomplish this, it features high fill power down, thin 10-denier Pertex Quantum shell fabric, and a tiny half-length zipper. A size regular tipped our scale at an impressive 1.49 pounds.

We were surprised, however, because this meant the Mythic was slightly heavier than a few other ultra-premium bags that felt warmer, were a size larger, and included burly full-length zippers. Overall, the Mythic is still ultralight, with a great warmth-to-weight ratio, but there a few higher performers.

rab mythic 400 backpacking sleeping bag review - when placed side-by-side with the western mountaineering megalite...
When placed side-by-side with the Western Mountaineering MegaLite (top), the Rab Mythic's sharper taper toward the feet (bottom) becomes more apparent.
Credit: Jack Cramer


One aspect of this bag that's sacrificed to achieve its low weight is its comfort. The Mythic 400 features some of the narrowest dimensions of any bag we tried. Testers specifically complained about the lower end of the bag feeling constrictive. We were big fans, however, of softness of its liner fabric and cozy loft of its premium down.

rab mythic 400 backpacking sleeping bag review - our entire review team noted this model's comfortable and nicely...
Our entire review team noted this model's comfortable and nicely articulated vaulted foot box.
Credit: Ian Nicholson

Packed Size

This bag is the only one in the review that comes with a waterproof stuff sack. Although this sack isn't quite as good at compressing the bag as an aftermarket compression sack, it performed better than the other simple drawstring stuff sacks we tried.

Using an aftermarket compression sack we measured its minimum compressed volume at 7.3 liters. This is better than average but not as small as its low weight would suggest.


The performance area most compromised by this bag's desire to be ultralight is its versatility. Our testers found the minimalist half-length zipper to be ineffective at venting excess heat on warmer nights.

In addition, the trapezoidal baffles that hold its down are not continuous. This eliminates the possibility of moving insulation from the top to the underside of the bag to adjust the level of warmth. Other ultra-premium bags with continuous horizontal baffles, like those from Feathered Friends and Western Mountaineering, thus possess a distinct versatility advantage.

Factoring these drawbacks in, we are most confident recommending the Mythic 400 for lightweight missions within a narrow temperature range of overnight lows between roughly 25° and 45°F.

rab mythic 400 backpacking sleeping bag review - the tiny weight-saving zipper on the rab mythic 400 is unfortunately...
The tiny weight-saving zipper on the Rab Mythic 400 is unfortunately prone to snagging.
Credit: Jack Cramer

Features and Design

This bag is clearly designed to be ultralight, and all superfluous features have been stripped away for this purpose. Despite these sacrifices, however, it still weighs a couple of ounces more than equal warm, but less expensive rivals. We still like the Mythic's high-quality materials and construction but feel like it doesn't strike a bullseye on what seems to be its overarching design goal.


Due to its ultra-premium down this bag comes with an ultra-premium price tag. However, compared to the other expensive bags the Mythic doesn't stack up particularly well. In fact, for most outdoor applications, our testers would prefer one of the other high-end bags. For this reason, we consider this bag to rank toward the bottom of the field in value.


The Rab Mythic 400 is ultimately a victim of the high expectations set by its high price. On its own, it's an incredibly light and well-made bag. But in direct comparison with other ultra-premium sleeping bags, its deficiencies in comfort and versatility become more apparent. As such we can only recommend it for ultralight travelers if they can find it on sale.

Jack Cramer

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