Thermarest Hyperion 20 UL Sleeping Bag Review

Tested and reviewed by Trek Scotland over three seasons [April to November] in the Scottish Highlands. This was our go-to sleeping bag for our Multi Day clients over the 2019 season. It was also used by one of our team members on her recent epic through hike of the Pacific Crest Trail.

We are always looking for the holy grail of Multi Day Trekking gear that goes beyond lightweight and enters the world of Ultra. When we first heard of the Thermarest Hyperion 20F/-6C Sleeping Bag the excitement levels within our team reached fever pitch. Would this be the sleeping bag that would take us and our clients into the world of true Ultra Lightweight?

First impressions of the Hyperion are striking. The pack weight in its stuff bag of just over 600g and with its stuffed size of 15 x 20 cm is mind blowingly light and small [Regular Size]. Once out of the bag the lofting starts to take place. This is somewhat magical and once the Hyperion is fully lofted you wonder how it ever fitted into such a small space. When totally lofted it is looks invitingly bulky, warm and protective. However, like most bags, to be completely lofted takes some time and we would recommend getting the bag out as soon as your tent or bivy is up, giving it a good shake and allowing at least 30 minutes before settling into it.

The fill weight of 345g of 900 fill Goose NikWak Hydrophobic Down with a box baffle construction are the key elements allowing a potentially amazing warmth to weight ratio and for this sleeping bag to be used on cold spring and autumn nights. Weight is also saved by only having a ‘skinny’ left sided half length zip which also keeps the foot and lower part of the body in a warmer zone. Further weight saving has been made by keeping the traditional mummy shape relatively narrow even though we found the general comfort fit for most people allowed ample room without feeling too constricted. With the hood fully tightened and baffled around the head and neck this gave a snug sleeping environment on cooler nights. However, those with very broad shoulders might find the bag quite constraining [145cm at the shoulders for the Regular]. The bag is multisex and comes in Small, Regular and Large Sizes.

Once we got the Hyperion up high in the mountains the big question was would this bag keep us and our clients warm? The reviews on this are mixed. In a nutshell for warm sleepers, generally men, the sleeping bag was more than ample for outdoor temperatures down to -0C. For cold sleepers, more clothes had to be worn and even then, some complained of cold spots, especially around the back, even though the bag uses mesh walls to maximize loft and minimize cold spots in key areas. Also, as a means to reducing weight and to compensate for compression against a sleeping mat [NeoAir Xlite in our case], most of the down is used on the top and sides of the sleeping bag with only 30% used on the underneath. This is great for back sleepers. To help side sleepers the bag comes with two relatively flimsy synergy straps to hold the bag in position to the sleeping mat. However, we found most of these broke at their attachment points and didn’t perform as intended. In relation to warmth, it also has to be taken into account that we always use a silk liner with our bags and, as with all sleeping bags, it makes a difference on how well fed people are, what they are wearing, what sleeping mat they are using [NeoAir Xlite in our case], and how cold or warm they are before getting into the Hyperion. Star jumps before bed are always good!

On occasions the foot area and top of the sleeping bags became damp due to tent/bivy condensation. This did not seem to impact on the Hyperion’s performance and the bag retained its insulating properties due to the water resistant qualities of the hydrophobic down and also due to the qualities of the 10D Nylon Ripstop outer. The outer has performed well in terms of being robust enough and allowing the bag to be wiped cleaned. In terms of durability, one team member used it continually over 5 months on the PCT… it is still going strong and she is looking forward to using it on another long through hike next year.

Our Verdict

The Therm-a-Rest Hyperion 20F/-6C is a ground breaking sleeping bag in terms of weight to warmth ratio. However, it will divide opinions on how warm it truly is. In our view if you generally run hot and sleep on your back then this is a brilliant three season sleeping bag that will lighten your pack significantly. For those who run cold this becomes more of a compromise and they might want to consider using a winter rated sleeping mat with it or pack more clothes to wear at night.

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...