This is a preview of a member exclusive premium article.


The Outdoor Research Stargazer AscentShell Bivy (18.9 oz / 536 g, $259) is of interest to alpinists, backpackers, and bikepackers because it is one of the few waterproof-breathable bivy sacks on the market that weigh just over a pound, has a side-entry zipper, and also includes mosquito netting and a headroom-extending pole.

Stargazer Bivy Stock Photo
Photo: Outdoor Research

About this Review

This review of the Outdoor Research Stargazer AscentShell Bivy is a Limited Review.

A couple of years ago, I started engaging in one or two-night winter backpacking trips, mainly in the White Mountains of NH. I first started with four-season tents, but the weight of those was around 5 lbs (5.25 kg) or more. Then I had a couple of overnighters in my winterized hammock. I was extremely satisfied with this setup considering its warmth, comfort, lack of condensation, and ease of entry and exit. However, I noticed that when heading to unknown locations, particularly in the Whites, sometimes finding the right trees took longer than expected.

I started thinking that a waterproof, breathable bivy may be the solution to unsatisfactory camping spots.

When using a bivy, if you have enough room to lay or, worst-case scenario, sit, then you have a place to sleep. We find ourselves in these locations typically in the summer, and so the mosquito netting and wide opening of the Outdoor Research Stargazer AscentShell Bivy are desirable when compared to other offerings.

I tested the bivy at Mount Washington State Forest in MA.  Conditions ranged from cold and dry (below freezing) to 44 F (6.6 C) with winds above 15 mph (24 km/h) most of the night (the maximum was 22 mph / 35.4 kph). I also had ample opportunity to test the Outdoor Research Stargazer AscentShell Bivy in rain ranging from drizzling to extended downpour.

Top down view of the Stargazer AscentShell Bivy.
The Outdoor Research Stargazer AscentShell Bivy during testing.

Features and Specifications

  • Enlarged head area
  • Side entry
  • Mosquito netting
  • Two stake loops
  • One guyline loop
  • Fully taped seams
  • Stuff sack (4 in x 4 in x 12 in / 10 cm x 10 cm x 30.5 cm)
  • Fabric: Ascentshell 3L, 100% nylon, 20D mechanical stretch ripstop face with 100% polyester 12D backer, 100% nylon, 40D ripstop with TPU lamination floor
  • Weight (claimed): 18.9 oz / 535 g
  • Weight (measured): 19.6 oz / 555 g (bivy 17.3 oz / 490 g, pole 1.8 oz / 51 g, stuff sack 0.5 oz / 14 g)
  • Dimensions (claimed)
    • length – width at the top – width at the bottom): 82 in – 26 in – 19.5 in / 208 cm – 66 cm – 49.5 cm
  • Dimensions (measured)
    • length – width at the top – width at the bottom: 77 in – 25 in – 19 in / 195.5 cm – 63.5 cm – 48.2 cm
  • Bathtub floor with a height of 2.75 in (7 cm)
  • Waist-length #3 zipper with a 1 in (2.5 cm) stiffened storm flap plus a second 3 in (7.6 cm) flap on the hood
  • Overhead pole sleeve and volumizing pole. The pole is 52.3 in (132.8 cm) in length. Once inserted, the base of the created arch is 29.3 in (74.4 cm), and the peak height is 18 in (45.7 cm)
  •  The length was measured along the right side, from the pole sleeve to the footbox seam. The width at the top was measured 5 in (12.7 cm) lower from the left pole sleeve and the bottom width was measured about 10 in / 25.4 cm from the footbox. Both measurements were made from floor seam to floor seam, not including the bathtub floor seams.
Vazquez Pole sleeve and velcro closure
Pole sleeve opens on one side only and is secured with velcro.

Performance Analysis

Since this is a Limited Review of the Outdoor Research Stargazer AscentShell Bivy, a detailed performance analysis based on long-term use will not be presented. Instead, performance observations and issues are noted below.

Vazquez Zipper guards
Notice the large flap that protects the zipper on the hood side (charcoal color).
CriteriaObservations and Issues
WaterproofnessThe Outdoor Research Stargazer AscentShell Bivy is constructed of two different fabrics: a proprietary waterproof breathable 3-layer top fabric labeled AscentShell and a TPU laminated floor. As usual, the seams are taped. The cut of the bivy includes additional seams to form a 2.75 in / 7 cm tall bathtub floor of sorts, which effectively raises the #3 zipper off the ground.

The zipper is well guarded against vertical water ingress. The top half is protected by a 1 in / 2.5 cm stiffened storm flap. Additionally, a second 3 in / 7.6 cm flap protects the other half of the zipper as it comes around to form the hood.

While the OR website does not publish any waterproofness numbers, in my experience, the fabric is waterproof. The water I found inside the bivy after my testing (some of which included intense rainstorms) was either the result of condensation or made its way in through a zipper opening.

I like leaving a roughly 6 in / 15.2 cm opening in the zipper as close to my mouth as possible. I have observed that spindrift and rain will splash my face on windy nights when laying on my back and leaving the opening at the apex. The solution for both situations was turning on my side and/or moving the opening to the side of the bivy.
Breathability / Air PermeabilityThe OR website does not publish any numbers on breathability or air permeability. At around 0 F (-17.8 C) , I did not experience much condensation in the bivy. The bivy was dry to the touch. Although my sleeping bag felt moist in my lower legs it was not enough to make my hands wet. It was certainly not wet enough to wring any water from the bag, nor wet enough to make my feet cold at night.

At around 45 F (7C) and all night rain, once again, my footbox was slightly wet. It was nothing I could wring out and nothing that manifested itself in any way while sleeping. But this time, I could feel the wetness in my hand when brushing the bag.

Based on my experience, the amount of moisture felt similar to what I experienced before in GoreTex bivies (military one and older Outdoor Research model) as well as the Montbell Sleeping Bag Cover. (See Compared To…)
WarmthThe bivy definitely provides an increase in warmth. On one testing evening, the night time forecast called for lows around 10 F ( -12.2 C). I brought my Enlightened Equipment Enigma 20 F (-6.7 C) down quilt, hoping that the bivy would suffice. And if it did not, I was planning to wear my down jacket and down pants to supplement. At the 9:30 p.m., the temperature was 15 F (-9.4 C). I decided to wear my down puffy jacket to bed, but I felt the pants were unnecessary. When I got up at 7:30 a.m. the next morning, I noticed it was much, much colder than the forecast had anticipated.

My backpack thermometer bottoms out at 0 F (-17.8 C), so I could not tell how cold it was. When my partner sprung out of his hammock at 9 a.m., he said the temperature was -10 F (-23.4) based on his thermometer.

At around 45 F and rainy, I ended up using a 100 weight fleece vest draped over my torso to supplement my Enlightened Equipment Revelation 40 F (4.4 C) down quilt. Experience tells me that the bivy was also trapping a significant amount of heat. In those conditions, I would typically use a 30 F (1.1 C) bag or additional clothing to supplement the Revelation quilt.
Comfort / RoominessSee Commentary
PackabilityThe original stuff sack that comes with the Outdoor Research Stargazer AscentShell Bivy allows it to pack into a 12 in x 4 in x 4 in (30.5 cm x 10.2 cm x 10.2 cm) package without much compression. My preference with bivies is to stuff them at home the night before leaving for a trip by inserting the pad and quilt or quilts into the bivy and then roll them into the bottom of my pack. This approach speeds up deployment and entry in case mosquitos or precipitation are a concern at bedtime.

For my winter outing, I was able to stuff the bivy + Thermarest NeoAir Xlite Regular (72 in x 20 in / 182.8 cm x 50.8cm) + Enlightened Equipment Enigma regular length and wide width 20F/-6.7 C into a bundle measuring 12 in x 7 in x 7 in (30.5 cm x 17.8 cm x 17.8 cm) without much compression. This is a really compact winter shelter setup, which, combined with a 0.5 in (1.3 cm) closed cell foam pad under the bivy, allowed me to sleep warm at nighttime temperatures below -10F (-23.3 C).


What makes the Outdoor Research Stargazer AscentShell Bivy Unique?

The fabric of the Outdoor Research Stargazer AscentShell Bivy provides the expected breathability and waterproofness. The mosquito netting and wide zippered opening allow its use in a wide array of conditions. Users who place their sleeping pads under the bivy will find the Stargazer AscentShell Bivy offers incredible performance. Users shorter than 6 ft (183 cm) in height or who have medium torsos who wish to place their sleeping pads inside will probably be equally happy. As I stated above, the Stargazer AscentShell Bivy can pair with other gear to form an incredibly compact cold-weather sleep system.

That being said, my biggest drawback is the Stargazer AscentShell Bivy’s size. My preference is for sleeping pads inside the bivy, which users of long or wide pads will struggle with. Having said that, I see myself using the Outdoor Research Stargazer AscentShell Bivy when air traveling in three seasons to locations with low night-time temperatures and the chance of evening/night-time rain. In particular, when visiting rocky areas with little room for tents. Its light weight, small packed size, and the option to have full protection when in a semi-seated position make it ideal for such trips.

Here are some of the features that I paid particularly close attention to while conducting my Limited Review.

  • Waterproofness and Breathability
  • Roominess and Comfort
  • My Wishlist

Waterproofness and Breathability

--- End of free preview ---
Member Exclusive

A Premium or Unlimited Membership* is required to view the rest of this article.


* A Basic Membership is required to view Member Q&A events