The world's most in-depth and scientific reviews of outdoor gear

How We Tested Ultralight Sleeping Bags

Monday November 4, 2019

Our latest review of Ultralight Sleeping Bags marks our eighth year of using, testing, and comparing these products in all seasons and conditions, all over the world. To bring you the best and most comprehensive review possible, we have built on our previous experiences of hiking on some of the most iconic trails in the world — the Appalachian Trail, Pacific Crest Trail, and Continental Divide Trail — as well as on mountain and trail adventures all over Colorado. We tested them in the field while trekking in the Khumbu, Makalu, and Manaslu regions of the Nepal Himalaya, in the deserts of southern Utah, and in the slowly thawing Rockies of Colorado and Wyoming.

A solo campsite up in a side valley of the Khumbu  the famous part of the Himalaya that is home to Mt. Everest. The 20 Degree by ZPacks kept us nice and warm on what proved to be a chilly night.
A solo campsite up in a side valley of the Khumbu, the famous part of the Himalaya that is home to Mt. Everest. The 20 Degree by ZPacks kept us nice and warm on what proved to be a chilly night.

To us, there's really only one way to test how a product truly performs - by using it. With this in mind, we tested these bags by sleeping in them - outside - a lot. We used them on windy desert nights and blizzards at 15,000 feet, and everything in between. Many people slept in each bag, and we've spent excellent and comfy nights in the wilderness, and shivered through enough sleepless nights to truly understand the meaning of "temperature ratings." One of our testers caught two colds that he blames on freezing all night in search of the truth about these sleeping bags. We went the extra mile to make sure we know what we're talking about, and we hope you find this review useful.

We test and write these reviews trying to be as objective and specific as possible, and try to cover the bases of how anyone might use these products. However, your goals may differ from ours, so be sure to take a look beyond the numbers to see what will work best for you.

Below we show you how we tested each product so that you can better understand the ratings we've given.

Comparing mummy bags on an extended road trip to the Bighorn Mountains in northern Wyoming. These are the blue Vireo UL  orange Patagonia 850  and purple WM HighLite.
Comparing mummy bags on an extended road trip to the Bighorn Mountains in northern Wyoming. These are the blue Vireo UL, orange Patagonia 850, and purple WM HighLite.

Warmth


For warmth, we rated each bag on its absolute warmth, ignoring the manufacturer's temperature ratings (which we found were not always very indicative of performance). To do this, we slept in these bags outside in the mountains during the cold spring months and the high desert in late October. The shoulder seasons in the high mountains of the Colorado Rockies, the Colorado Plateau, and the Himalayas are not warm, so we came to understand how well these bags worked by suffering in them. Many people have slept in each bag, and we kept notes on where we slept and what the overnight low was and compared them to how we felt and what clothing we wore inside the bags. This information helped paint us a clear picture about warmth, but to attempt to verify our findings objectively, we performed the ice bottle test, where we put an entirely frozen Nalgene water bottle inside each bag and left them lying in the shade on a hot day for an hour. We then made a note of how much the ice had melted during that time to help us fine-tune our understanding of which bags were the most insulated. We further amended our opinions by analyzing the function of heat-trapping features(or lack thereof), such as draft tubes, fully enclosed zippers, neck baffles, type of baffle construction, and hoods.

Here we put a completely frozen Nalgene bottle into the inside of the WM HighLite  then zipped it up tight and left it in the shade on a hot day for an hour  in order to compare the relative insulating properties of the various sleeping bags. We performed this test with all the sleeping bags in this review.
Here we put a completely frozen Nalgene bottle into the inside of the WM HighLite, then zipped it up tight and left it in the shade on a hot day for an hour, in order to compare the relative insulating properties of the various sleeping bags. We performed this test with all the sleeping bags in this review.

Weight


To test for weight, we took each product and weighed it on our independent scale, accurate down to 1/100th of an ounce. Sometimes the readings matched the manufacturer's listed weight; sometimes it didn't. We included all integral pad straps and attachment parts, but we did not factor in the weight of stuff sacks, although those are listed on the specs table. Lower weights scored higher.

Comfort


When it came to comfort, field testing was once again our bread and butter for determining what worked and what didn't. To ensure objective testing, we had multiple people use each bag and discuss their opinions afterward. A primary consideration was the fit of a bag, and we ordered all bags to the same size specifications so that we could compare them fairly. We attempted to assess for how loose or restrictive a bag was, how pleasant the interior fabric felt against skin and clothing, and whether features like Velcro, zippers, or drawcords affected the comfort level.

After the gear has dried out  why not compare some quilts in the sun! Here assessing the relative similarities and differences between the Backcountry Quilt 700 and the Katabatic Palisade 30  in Nepal.
After the gear has dried out, why not compare some quilts in the sun! Here assessing the relative similarities and differences between the Backcountry Quilt 700 and the Katabatic Palisade 30, in Nepal.

Versatility


When it came to assessing versatility, we first attempted to identify how many different situations a bag could be appropriately used in, and then did our best to test the bag in all those conditions. Our countless nights out in the field were essential for determining how truly versatile a sleeping bag was. For quilts or blankets that had the option of sleeping wrapped up, attached to a pad, or fully spread out, we slept in them each way.

In May in the Dark Canyon Wilderness area in Utah  we experience low temperatures at night in the mid to upper 50s and were perfectly comfortable without a bunch of extra clothes in the Spark I.
In May in the Dark Canyon Wilderness area in Utah, we experience low temperatures at night in the mid to upper 50s and were perfectly comfortable without a bunch of extra clothes in the Spark I.

Features


It is easy to take a new sleeping bag out of the box at home and start to play around with it, but not so apparent is whether the neck cinch cord will really stay tightly cinched around your neck all night when you are cold, or whether the hood truly covers your entire head and forehead comfortably, or whether the pad straps will stay fastened and tight all night, rather than coming loose and allowing in cold air. The only way to truly know these things is to test them in the field, which is what we did, over and over again.

The Flicker 40 is one the quilts in the review that is capable of opening up fully into a blanket on warmer nights. It's wide enough for two people to fit under.
The Flicker 40 is one the quilts in the review that is capable of opening up fully into a blanket on warmer nights. It's wide enough for two people to fit under.