The Big Agnes Bolten is a 20-degree, standard mummy-style, synthetic sleeping bag. It breaks from convention with the inclusion of stretchy panels that run the length of the bag on either side, enhancing the comfort, fit, and mobility of the bag.

Weight

Big Agnes lists the Bolten as weighing 2 pounds 11 ounces. On our scale we measured 2 pound 15 ounces, which is rather hefty. It weighs more than all of the other three-season bags in this test, and therefore this bag would not be our first choice for lightweight backpacking or climbing missions. High weight and low compressibility are the main downsides to this bag, but everything else is great. We think this bag is comfortable, weather resistant, and very well made. The trade-off for all of those other things is a slightly higher weight. It is up to each consumer to decide which metrics are the most important for their camping style. We loved sleeping in the Bolten. For car camping or wet conditions, we were eager to pull this one out.

Compressibility

Along with a high weight, the compressibility of this bag is not stellar. It comes with a nylon stuff sack, but that sack does not have compression straps. The bag could be packed into a smaller package with an after-market compression sack. In the included stuff sack the packed size is 8×17.5 inches, which is one of the largest in our test. The large size makes the Bolten a little unwieldy for backpacking, but synthetic bags tend to be a little bulky. In wet conditions, the extra weight and bulk will be offset by the continued loft of the water-resistant insulation.

Warmth

One night during our testing period we had two testers sleep side-by-side in the same tent in the two synthetic bags in this test, the Big Agnes Bolten and The North Face Hyper Cat. It was a cool spring night near Tahoe, California at approximately 6,000 feet of elevation. In the morning the tester in the Hyper Cat reported being uncomfortably cold and shivering most of the night, while the tester in the Bolten reported being perfectly comfortable and sleeping like a log. Though this is informal and unscientific, our sense of this bag is that it is warmer and cozier than its main competitor in this review.

This bag is filled mostly with Primaloft Silver insulation, with Primaloft Gold Active insulation along the sides. These are both top-tier synthetic insulations. Synthetic sleeping bags have their place. Though heavier and bulkier than down, when camping in drizzly spring weather, the notoriously damp Pacific Northwest, or in a wet late-season snowstorm, being curled inside a blanket of insulation that won’t collapse at the first drop of moisture is extremely comforting – and safer. One of our testers took this bag with her on a climbing trip to Cochamo, Argentina, a rainforest where it, well, rains. She felt that this was the most comfortable and warmest choice for that type of trip and much preferred this bag to any down alternative.

Ventilation

With a traditional mummy shape, the Bolten doesn’t offer much ventilation besides unzipping the side zipper. Unlike on The North Face Hyper Cat, which has a half-length front zipper, the Bolten’s side zipper is full length, which does allow the bag to open for a relieving breath of fresh air. The zipper really does reach all the way to the toe of the bag. The two-way zipper allows you to keep it zipped by your shoulders but open for venting at your feet.

Features

The most appealing feature of the Bolten is the stretchy side panels that start at the collar and run the entire length of the bag on both the left and the right. The face material is a polyester spandex stretch fabric that is soft to the touch, and this material also lines the stretch panels on the interior of the bag. This is a very cozy next-to-skin feeling. Additionally, the insulation within these panels is different from that in the rest of the bag. It is filled with Primaloft Gold Active Stretch Insulation, which provides four-way stretch while keeping the occupant warm. These panels allow the sleeper to roll over, point legs and elbows to the side, and squirm around without feeling restricted or confined inside the mummy shape, but it maintains the efficient warmth conservation of a mummy bag.

The other notable features of this bag are the thick draft collar, which seals in warmth around the neck, and the snuggly hood with a one-handed cinch. Some hoods have cinches that go around the head in two directions, circling the neck and the face, but the Bolten keeps it simple with just once cinch to close the opening around the face.

Lastly, this bag has loops included on the interior for attaching a sleeping bag liner and loops on the exterior to make it easy to hang, store, or dry out; more small details that make this bag easy to use.

Durability

After using the Bolten during several tent camping trips in the mountains of California and a weeklong rainy #vanlife trip outside Yosemite National Park, we recognized that this bag is well crafted and high quality. From the rolled edge of the zipper and the easy to grab zipper pulls to the tapering stretch panels the single-cinch hood with plush draft collar, every detail is well thought out, and every seam is meticulously sewn. One detail in particular that we came to appreciate is the stiff fabric sewn underneath the nylon face material along the length of the zipper. This made it so that the zipper almost never snagged, enhancing the ease of use and reducing the likelihood that the zipper would tear the fragile nylon material. We believe that this bag will last quite a while.

The limiting factor for the Bolten’s durability, which would be the same for any synthetic insulated bag, is how many compressions and expansions the insulation can take. Man-made insulation doesn’t have the same longevity that down insulation does, but we are still confident that the Primaloft inside this bag will last multiple seasons before becoming noticeably less lofty.