For the minimalist backpackers, thru-hikers, and mountaineering crowd, lightweight gear is paramount. In 2021, the Western Mountaineering TerraLite 25 is my top ultralight pick. It’s made in the USA and insulated with 850+ fill power premium goose down. This is a part of the ExtremeLite™ series from Western Mountaineering.
As a matter of fact, the only other company in the same class as WM is a brand called Feathered Friends. The construction details and feather down quality from these two are absolutely unmatched. But for stomach or side sleepers I prefer the comfort the TerraLite 25 offers.
Like the other premium down bags from on the market, most are warm, lightweight and packable. Yet unlike the others, the TerraLite 25 is wider and perfect for resting on your side or tummy. In fact, its wide enough to get your arms inside and tuck up your knees, even for bigger users.
Wide Modified Mummy-Bag
The semi-rectangular shape of the TerraLite 25 is as roomy as it needs to be. Its large, but not too large that I can roll around and move my legs with ease. In the winter, you can use it down to below 20 degrees wearing a down jacket inside without constriction. The shape is wide in the chest/hips and tapers at the feet but is still wider that classic mummy-style bags.
Durability is of this backpacking sleeping bag is decent, the outer-shell is a 12 denier ripstop nylon shell. The whole point of this sleeping bag is to excel in compressibility and weight. As a result, you have to accept a few points lost somewhere. To help, the shell has great water resistance by adding a DWR (Durable Water Repellent). By placing a finish on the shell it blocks out condensation from tent walls. Plus, over time you can reapply this finish if it begins to wear.
Inside Western Mountaineering uses 15 denier nylon taffeta. On my bare skin it feels airy, plush and soft which is pleasant compared to others in this category.
Meanwhile, it uses a full-length dual zipper so you can snake out your feet when it gets warm out. As well as mate to another sleeping bag to create a double bag. Another bonus is to completely unzip it to use as a quilt/comforter in a hammock. The big plus for the zipper is the wide tape facing it, this makes the zippers pretty much snag proof.
Superior Warmth Performance
Western Mountaineering made some magic for how much warmth this bag retains. This is due to the continuous horizontal baffle construction it employs. To explain, the feather down insulation is inside continuous fabric tubes, or baffles. The baffles for the TerraLite 25 sit perpendicular to the length of the bag. Using this type of design allows you to move feathers to the top or bottom of the bag. For example, on cold nights you can shift feathers up to your chest to trap extra heat. The opposite is true for warmer nights, push it down to your calf and poke out your feet.
The main reason for the performance is the absolute quality of the insulation. Western Mountaineering didn’t cut any corners in production. Inside the TerraLite 25 is 850+ fill power goose feather down. This is the lightest and most compressible down available. The best quality down lasts longer at the original temperature range thus the value is there. The TerraLite boasts an EN limit rating of 22 F (-6 C) and an EN comfort rating of 20 F (-7 C).
Next, the insulated hood with adjustable draw closure keeps heat next to your face. I especially appreciate the 3-D down filled draft tube, it really helps to keep the cold out.
Beyond the shape and insulation quality, the other vital factor for this bag is the weight. It weighs under two pounds, but is no compromise in comfort. Plus it packs down to an impressive 7-inches by 13-inches, that is tiny!
The obvious con for some buyers is going to be the price, this is an expensive sleeping bag. But the reason for this is the material quality and weight. You simply can’t get a premium ultralight 3-season sleeping bag for cheaper.
Second, is Western Mountaineering doesn’t use a sleeping pad sleeve under the bag. While the TerraLite 25 doesn’t slide around much as I sleep, using a pad underneath is my preference. You should bring a sleeping pad with a good r-value to insulate you from the cold ground. For the purpose of being a lightweight backpacking bag though, losing the pad sleeve helps drop the total weight. I classify this as more of a personal feature I wish it had, than an actual downside.
The last problem I have with this sleeping bag is the lack of a draft collar. If Western Mountaineering decide to add one, this sleeping bag would be perfection.
Buy the Western Mountaineering TerraLite 25 if you are a side sleeping ultralight enthusiast. Doing so gets you the best insulation, lightest-weight, the warmest sleep gear you could ever want.