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
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.
Warmth
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 felt this rating was accurate compared to other EN-rated bags. However, the unrated Western Mountaineering MegaLite and Feathered Friends Merlin, which both receive 30° ratings from their makers, seemed to be slightly warmer.
Weight
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 size long Feathered Friends Merlin—a warmer bag that also includes a burly full-length zipper. Overall, the Mythic is still ultralight, with an outstanding warmth-to-weight ratio, but the even lighter Merlin bests it.
When placed side-by-side with the Western Mountaineering MegaLite (top), the Rab Mythic's sharper taper toward the feet (bottom) becomes more apparent.
Comfort
One aspect of this bag that's compromised 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.
Our entire review team noted this model's comfortable and nicely articulated vaulted foot box.
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 after-market compression sack, it performed better than the other simple drawstring stuff sacks we tried.
Using an after-market 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.
Versatility
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 down from the top to the underside of the bag to adjust the level of insulation. Other ultra-premium bags with continuous horizontal baffles, like those from Feathered Friends, Western Mountaineering, and Marmot, possess a distinct versatility advantage.
Factoring these drawbacks in, we are most comfortable recommending the Mythic 400 for lightweight missions within a narrow temperature range of overnight lows between roughly 25° and 45°F.
The tiny weight-saving zipper on the Rab Mythic 400 is unfortunately prone to snagging.
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 the warmer, cheaper, and more versatile Feathered Friends Merlin. 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 over-arching design goal.
Best Applications
The Mythic is ideal for any application where you hope to go truly ultralight. For thru-hikes or other long trips, however, its versatility limitations might be frustrating to deal with.
Value
Due to its ultra-premium down this bag comes with an ultra-premium price tag. However, compared to the other $400+ 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 stuff sack in value.
Conclusion
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.
