Tested by Trek Scotland between the months of September through to December 2019.

The first point we need to raise for this review is that with receiving a prototype we can only write about the Ultra Mythic 180 in this current form. We would expect the final product to have slight differences in weight and design. Also, the EN temperature ratings are currently only estimates and taken using fill weight just below 180g.

We had heard rumors that Rab were due to launch a new line of sleeping bag, in which the weight-to-warmth ratio was off the scale. We are big fans of the Mythic series and have found them to be very dependable for when you want to keep your pack weight down without compromising on warmth. So, what a pleasant surprise it was to find out we would be receiving a prototype of the Rab Ultra Mythic 180. At 400 grams and packing smaller than some of our lightweight air mats it's instantly recognisable that if this is the future of sleeping bags, then gone are the days when this item was considered one of the larger essentials for your pack. The Rab Ultra Mythic 180 is incredibly packable for its weight-to-warmth ratio. 900+ fill power goose down means that once you give the Ultra Mythic 180 time to loft, it dramatically changes shape and size, bringing back confidence that this truly is a bag built for 3-season use.

TILT technology is the real breakthrough element of the Rab Ultra Mythic and to the eye appears very similar to the reflective lining used throughout several bags currently on the market. Thermo Ionic Lining Technology behaves in a slightly different way as it is coated at fiber level with titanium. This cuts down radiant heat loss, with claims that the liner can increase the bags temperature by around 30%. One of the issues with giving an accurate EN temperature rating for a bag such at the Ultra Mythic is that during temperature tests radiant heat cannot be measured due to the use of a mannequin. At this current time Rab have made an estimate of a comfort limit rating of 0 degrees, although once they hit the shelves an official rating will be established. Choosing the correct bag is already a hard process and although temperature guidelines do offer some help it’s a very individual choice that can differ on many factors and most people will find out only through first hand experience what works and what doesn’t.

Our guide using the Ultra Mythic 180 can be considered as a warm sleeper, 5’ 7” in height, medium build, and always had a meal or a hot drink shortly before getting inside the bag. Over 6 nights in total we found that the Ultra Mythic 180 worked comfortably for us at around 2 degrees while paired with a lightweight air mat with an R-Valve rating of around 3.8 (Sea to Summit Ether Light XT), with the bag only verging on the cold side on nights when the temperatures dropped to around freezing. The total weight of the bag and mat came in at 825 grams and stays close to Rab’s estimated comfort limit of around 0.

Using a lighter mat with a decreased R-Valve rating (Thermarest Neo Air Uberlight), and with the Ultra Mythic using less down, the underneath area, once compacted, was a noticeable cold area. Although in mid-summer we believe this combination would work fine taking the total weight of a bag and mat right down to around 650 grams.

As the temperatures started to drop, we paired an old 4-season bag with the Ultra Mythic 180 to give it an extra boost. Many people like to pair up bags in winter for reasons such as having a down and synthetic combo. This again is always a personal preference and with the Ultra Mythic 180 weighing nearly the same as our choice of winter liner, but with a much better warmth rating, it became a no-brainer to use it for this reason.

The trapezoidal chamber design helps to eliminated cold spots as, when compressed the stitching does not line up together. The design also prevents the goose down from moving too much. This is a construction mostly adopted within lightweight summer bags as it also uses less stitching throughout keeping weight to a minimum, and from previous experience using this style of baffle, as expected, does a good job.

The internal collar and hood are one of our favourite features found throughout most of Rab’s sleeping bags, and the Ultra Mythic is of no exception. Decent tension cords which aren’t too small of fiddly to use meant that all of our body heat was trapped inside working with the TILT lining to perform as efficiently as possible.

Rab’s fluorocarbon hydrophobic down developed with Nikwax does a decent job at resisting moisture with us only noticing slight dampness when used within a bivy. A small amount of clumping at the foot box led to a slight reduction of warmth in that area, but nothing that became uncomfortable. One of the advantages from using less down paired with the TILT lining is that it takes less time to air out and dry your bag. This not only saves time whilst out on extended expeditions but also gives you peace of mind that in the unfortunate event that the bag did succumb to excessive dampness the TILT lining and treated down should fair up much better than just standard down alone at retaining insulating properties.

With a minimalist nature in mind there are some sacrifices and dis-comforts you must live with to save those precious grams. The first being the 7D ripstop nylon outer. This material is very thin, so extra care is needed especially whilst at camp. We used a tough dry bag to store it in our pack, making sure it was kept away from any sharp objects, and the same was applied whilst working at our shelter. This sounds like common sense, but mistakes do happen. Just remember to treat the Ultra Mythic with that extra bit of care and attention.

The 1/8 length zipper might not be for all and offers next to no ventilation for use on warmer nights. Getting in and out is also a bit of a pain and once inside, the Ultra Mythic 180 can be regarded as a tight fit. For our shorter guide there was enough room to move around and have a comfortable night’s sleep although if you fall into the taller bracket (much over 6 feet) you may find the Ultra Mythic 180 to be a bit restrictive. Hopefully a long version will be available once they reach full production.

Our Verdict

Rab have always been regarded as producers of innovative sleeping bags at the highest quality. The Ultra Mythic 180 only backs up this claim with the standout feature being the TILT liner. Boosting the bags warmth by around 30% meant that less down is required, so at 400 grams and packing down to the similar size of a bag at nearly half its warmth rating makes for a minimalist’s dream item. The low weight does mean that a 1/8 zipper and tighter fit is required to save on those precious grams. Also, the reduction in down meant that the underside will compress during use, so a suitable mat is needed to help the Ultra Mythic reach its intended warmth rating. We believe this is just the start for a new standard of sleeping bags and expect this type of liner to become common place in the near future, not only just to save weight but also on an ethical scale in reducing the amount of down needed. Some have tried to use a similar approach already but Rab’s use of TILT, utilizing titanium at fibre level, has certainly performed much more efficiently. The estimated comfort limit of 0 degrees, we believe, is achievable if you are a warm sleeper although a slightly heavier Ultra 360 version will also be available with an estimated rating of -7. If we decided to use these for our clients, we would certainly opt for the 360 version as it also has a longer zipper providing easier access and comfort.

Trek Scotland is a small family business based in the picturesque village of Tomintoul in the North East region of the Cairngorms National Park. They provide bespoke Mountain Guiding for Single Day Walks and Lightweight Multiday Trekking experiences, including wild camping, in the stunning Cairngorms wilderness and surrounding areas. Whether in the high mountains or lower valleys, their Multiday Treks are equipped with high quality, lightweight camping and trekking gear. They only work with small groups and, whatever your ability, pride themselves on designing your outdoor experience completely to your needs and with professional guidance and expertise. Adventure is waiting...