Rab Mythic G Review: A 277g Down Jacket Built Around Warmth-to-Weight

Introduction

Rab has been building down products for more than 40 years, a history that began with Rab Carrington making down jackets and sleeping bags at home in Sheffield. The Mythic G is the latest iteration of that work, and it is positioned as the brand’s most impressive warmth-to-weight jacket rather than simply its warmest.

That distinction shapes everything about the design. This is not a jacket built to win a warmth contest against heavyweight expedition layers. It is built to deliver a serious amount of insulation at the lowest possible weight and packed volume, and the specifications are unusual: 277g in a medium, 1,000 fill power down, and a feature set pared back to almost nothing.

The useful question is who benefits from that trade-off, and where a jacket like this stops making sense.

Who This Jacket Is For

The Mythic G suits people who count grams and pack space: climbers moving fast on alpine routes, runners and fastpackers who want a just-in-case layer, and anyone who needs dependable warmth in a package small enough to forget about.

It clips to a harness, disappears into a running sack or a rucksack, and takes up very little room when compressed. For a day out where you simply want warmth available without carrying weight, that combination is hard to argue with. It has also proven itself as an emergency layer during an unplanned bivouac on an alpine route, where it made a substantial difference to the night.

The other side of that coin deserves equal clarity. This is not an everyday jacket. It is not something to walk around a rainy national park in, and it is not designed as a belay jacket for standing around at a stance with a harness on.

Warmth-to-Weight: What the Numbers Mean

The headline figure is 277g in a medium. Alongside that, the jacket uses 1,000 fill power down, and there is 127g of it in the jacket.

Fill power is widely misunderstood, so it is worth separating two ideas. Fill power describes how much volume a given weight of down can fill, which is what allows a jacket to stay light and pack down small. It is not the same as warmth. A heavier, lower fill power jacket can still be warmer overall, simply because it contains more down. What 1,000 fill power buys here is efficiency: a large amount of loft for very little mass, so the jacket compresses into a small space and barely registers in a pack. As fill power goes, 1,000 is about as high as it gets.

How the TILT Lining Works

Inside, the Mythic G uses a silver lining that Rab calls TILT, short for Thermo Ionic Lining Technology. In practice it is a thin metallic layer that reflects body heat back toward the wearer, and Rab states it retains around 30 percent more radiant heat than a conventional lining, with no additional weight.

The effect is noticeable in use. Many down jackets take a while to warm the air trapped around the body, whereas this one feels warm almost immediately and continues to build as the down loft fills out. TILT has appeared across other jackets in the Mythic range, but this is the first time it has been paired with 1,000 fill power down.

The lining is also body mapped rather than applied uniformly. There is less of it under the arms, so if you do end up working hard in the jacket, that area is less likely to overheat and turn clammy.

Fabric and Feature Set: Deliberately Minimal

The face fabric is a 7 denier Atmos material, which is extremely thin. It handles normal abrasion reasonably well, but it is not intended for scraping through brambles or heavy brush.

Almost everything else has been stripped away in the name of weight. There are hand pockets, and the cuffs, hem and hood are all soft and non-adjustable so the jacket can compress as small as possible. There is no zips or hardware where they are not needed, which also helps it pack down further.

One exception is a pull cord at the waist. Hem adjustment is often removed on jackets like this, and keeping it here is a sensible call: without it, gusts can blow up under the hem. That is a small weight penalty worth accepting.

What to Consider Before Buying

The most important thing to understand is that the Mythic G is a specialist layer, not an all-rounder. It is not built as a belay jacket: the face fabric is not burly enough for standing around in, there is no two-way zip, and the hood is not helmet compatible. If you want a jacket to wear over a harness at a stance, this is not the one.

It is also not a rain jacket, and not a jacket for walking around in wet conditions. The thin face fabric and the down fill both mean moisture is the enemy.

Sizing is worth checking before you order. The jacket in question was a medium, and a 6 foot 4 inch frame would typically take a large.

Finally, think about how you will actually carry it. The Mythic G is designed to be clipped to a harness, shoved into a running sack, or kept in a rucksack for the walk you did not expect to need it on. If it will live in a pack as insurance, it earns its place easily.

Buying Advice

Buy the Mythic G if warmth per gram is your priority and you already own a shell and a burlier insulating layer for the conditions where this one stops being appropriate. It works best as part of a system: a thin, highly efficient layer for cold, dry conditions and fast, light movement.

It is less compelling as a first down jacket. If you want one jacket to cover commuting, wet walks and cold belays, a heavier face fabric and more adjustability will serve you better.

For anyone who has ever left a warm layer at home because of the weight, the Mythic G is the argument against doing that again. It packs small enough to bring along without thinking about it.

Where it fits in a kit list is straightforward: a lightweight warmth layer for the moments when you stop moving, the temperature drops, or the plan changes.

Conclusion

The Mythic G is a focused piece of kit. Four decades of down manufacturing show up in the details, from the 1,000 fill power down and the heat-reflecting TILT lining to the decision to remove almost every adjustable feature in pursuit of a 277g weight. It is not the warmest jacket in the range, and it is not meant to be. It is the one that delivers the most warmth for the least weight and pack space, and for fast and light use in cold, dry conditions, that is exactly the point.