The sun dipped below the horizon, and I was set to sleep on top of Wetterhorn Peak at 14,021 feet. Deep in the mountains of Colorado, I was putting my sleeping bag system to a real stress test: Would I be able to stay warm enough at the equivalent elevation of Camp 3 on Denali? All signs were pointing to yes, as my Rab Mythic Ultra 180 Sleeping Bag had a trick up its sleeve: titanium.

　　Similar to how an emergency blanket reflects heat, the Mythic Ultra uses a super-thin titanium coating on the interior of the bag to really bump up the BTUs — and boy, does it work. Complementing this is a high-loft 900 down fill, 10-denier fabrics, and expertly designed baffles, making the Mythic Ultra one of the best sleeping bag options on the market for those who enjoy packing light.

　　I took the Ultra Mythic 180 into the coldest environments I could this summer and came away confident that this was the new bag for me. No cold spots, no hot spots, and a well-fitted foot box; consider me impressed with my three sticking points.

　　In short: The Rab Mythic Ultra 180 ($600) is a superbly designed sleeping bag that hits all the marks for someone trying to go light while staying warm. Utilizing a proprietary titanium coating that reflects heat without sacrificing breathability, the Mythic Ultra 180 is a step ahead of other sleeping bags and might be the game-changer I’ve been looking for.

　　Looking for a new sleeping bag? Check out how the Mythic Ultra compares to the rest of the market in GearJunkies Best Backpacking Sleeping Bag Buyers Guide.

　　Rab Mythic Ultra Sleeping Bag Check 18° Price at REICheck 32° Price at REICheck 32° Price at Backcountry

　　7.7 How we rate products Specifications Shell fabric: 10-denier recycled ripstop nylon Available temperature ratings: 18°, 32°F (tested) Available sizes: Regular, long Tested packed volume: 2.7 L Tested weight: 14.1 oz. Tested fill weight: 6.3 oz. Insulation: 900-fill down Pros Titanium-infused inner lining reflects body heat back to you Insanely packable at ~3 L compressed 900-fill power down is very warm and compressible Less than a pound Cons Zipper is quite short at 9.5 (in the 32-degree version) Expensive Ian Atkinson Rab Mythic Ultra 180 Sleeping Bag: Review

　　The TILT titanium coating on the inside of the Mythic Ultra adds an impressive amount of warmth without becoming clammy; (photo/Ian Atkinson) Titanium-Powered Warmth? When it comes to a sleeping bag, Im always primarily concerned with warmth. This can come down to personal preference, as some people sleep cold and some sleep hot (like me).

　　Because of my natural tendency, I was able to push the limits of the Mythic Ultra 180 (a 28-degree comfort/18-degree lower limit rated bag) with some confidence, but is it truly a warm bag? For the weight, I would say yes.

　　The headline here is the Thermo Ionic Lining Technology (TILT), a reflective titanium coating that bounces heat back into the bag. My main concern here was whether this coating is breathable enough not to trap moisture and reduce the effectiveness of the down. Thankfully, I found the bag never got wet during my use, even in a fully enclosed shelter and camping near a river.

　　This is truly a game-changer, as anyone would know who has spent time huddled in a space blanket, warm yet soaked to the bone. But it seems that Rab has hit the mark here with adding some warmth with the most minimal weight penalty, and the brand has even expanded to using the tech in its high alpine insulation apparel, such as the Mythic Ultra Jacket weve reviewed previously.

　　Bag Construction and Cut

　　The baffle design on the Mythic Ultra is a savvy cut that didnt form any cold spots during my testing; (photo/Ian Atkinson) After warmth, I look at the baffle construction and cut on any new sleeping bag I jump into. Compression of down via your sleeping position can cause the loft to collapse, meaning minimal warmth can be collected by the bag. This often happens for me near my butt and knees when sleeping on my side and my shoulders when sleeping on my back.

　　The Mythic Ultra, however, is one of the few sleeping bags in which I didn’t develop cold spots. This is owed to the expertly engineered baffles and differential cut.

　　A differential cut is a feature where the inner fabric circumference is cut smaller than the outer fabric. This means that when you press the inside of the bag taut, it does not compress the outer layer, helping to retain loft.

　　Finally, this sleeping bag sports an angled foot box with an emphasis on comfort. I’ve had some poor experiences in the past with tight foot boxes, causing my calves to contract all night — not fun when trying to recover. I was pleased to find that Rab considered this in its design and made sure the foot box was snug without constricting the feet into an unnatural position.

　　An Unreal Packed Size

　　The Mythic Ultra is a super-compact bag, and I could get it as small as 2.7 L when compressed; (photo/Ian Atkinson) The Mythic Ultra 180 is wildly light and packable for the amount of warmth it can deliver, and uses a 900-fill power goose down. Down produces warmth by the amount of air it is able to trap within its loft, and the fill rating quantifies its ability to loft to a certain volume after compression.

　　900 fill is top of the line, and it compresses much better than the 650 or 700 fill downs commonly used in other backpacking sleeping bags. In fact, during my bench testing, I discovered that the Mythic Ultra 180 can be compressed to a mere 2.7 L! This type of packability is important to me, as I often find myself packing into the backcountry with a 36L pack, meaning every inch of volume is needed.

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　　Sustainable Build

　　The Atmos fabric used in the Mythic Ultra is 99% recycled, and treated with PFAS-free DWR; (photo/Ian Atkinson) Not only is the Rab Mythic Ultra 180 designed exceptionally well for comfort, warmth, weight, and packability, but it is made with recycled fabrics and a fluorocarbon-free DWR treatment. You wouldn’t know it by touch or sight, but the ultralight 10-denier Atmos fabric is made of 99% recycled material, and the DWR treatment for water repellency is free of any PFAS “forever chemicals.” 

　　Props to Rab here for making these decisions based on sustainability and the environment — it really shows they are trying to be an industry leader in more ways than one, and that you dont have to give up these metrics to score high marks in warmth and weight.

　　Short-Sheeted by the Zipper

　　The 9.5 entrance zipper on the Mythic Ultra 180 is comically small, and provides just enough space to wriggle into the bag; (photo/Ian Atkinson) My complaints are limited to only one with the Mythic Ultra 180: a tight fit when getting into and out of the bag due to the short 9.5-inch-long entrance zipper. I unfortunately found myself putting undue stress on the stitching multiple times, and even once, I felt like I might have popped a stitch. As a 6’0” 190-pound human, it would be tough to recommend the regular-sized bag to anyone larger than me. 

　　I will note that this is an issue unique to only the 30-degree version of this sleeping bag, as the 20-degree cut hosts a half-length zipper. Still a bit short, but much more room to get in and out of the bag.

　　If I could suggest any changes, it would be making the entrance zipper at least 6 inches longer and adding a second zipper pull — the weight penalty would be minimal and the ingress would be easier.

　　Rab Mythic Ultra 180 Sleeping Bag: Conclusion

　　The Rab Mythic Ultra 180 is an ideal bag if youre concerned with going lightweight while backpacking; (photo/Ian Atkinson) All in all, I’ve loved my time so far with the Rab Mythic Ultra 180. It’s warm for the weight, packable, ultralight, and made with sustainable materials. It managed to quell my concern of cold spots and tight foot boxes, and it kept me comfy on the summit of not one but two 14,000-foot peaks here in Colorado. 

　　The Mythic Ultra 180 is made for thru-hikers, fastpackers, bikepackers, and mountaineers alike who prioritize weight and packability while staying warm. It’s also perfect for folks who are looking to invest in a sustainable sleeping setup given the recycled fabric and PFAS-free DWR treatment.

　　If you’re looking for something more affordable and don’t mind the extra weight or volume, you might find the budget Kelty Cosmic Down 20 or Mountain Hardwear Bishop Pass 15 a better fit. For exceptionally cold sleepers, you’d want to find a bag that leans further into the warmth versus weight side of the spectrum.

　　Outside of those cases, however, the Rab Mythic Ultra 180 is a bag well worth the consideration, and will undoubtedly be my personal sleeping choice for years to come.

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