Outdoor Research Interstellar Bivy

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MSRP: $275.00
Current Retail: $275.00
Historic Range: $178.72-$275.00

Ascentshell 3L, 100% nylon, 20D mechanical stretch ripstop face with 100% polyester 12D backer, 100% nylon, 40D ripstop with TPU lamination floor

5-star: 0
4-star: 1
3-star: 0
2-star: 0
1-star: 0

Jake W TOP 25 REVIEWER REVIEW CORPS +6,538
October 14, 2019 | updated Oct 25, 2019

The Outdoor Research Interstellar Bivy is a four-season packable, lightweight bivy that utilizes OR’s highly successful AscentShell to boast incredible breathability, even in the clammiest of situations, while remaining waterproof. At only 23 ounces (with the option to leave the pole at home and go even lighter, around 19 ounces for the bivy alone), and packing to roughly the same size as your one-litre Nalgene it is a great option for fast and light, UL, or trips where camp space may be minimal.

 
Bivies are great for when you've arrived into camp late, and don't want the hassle of a tent setup!


Weather Resistance and Breathability 
The Interstellar Bivy utilizes Outdoor Research’s proprietary three-layer membrane, AscentShell, to create a waterproof/windproof barrier between you and the elements. According to O.R. AscentShell is created “by an electrospinning process where charged polymers are affixed to a grounded surface. Those polymers gather into a breathable membrane that, under a microscope, you can see forming a web that allows sweat vapors out but stops water from coming in.”
I can attest to the waterproof qualities of this bivy as I have slept through nights of rainstorms without a drop entering. The first day I received the bivy I laid it out in the backyard, got in, put the hose on the jet nozzle and gave it to my kids. The laughed hysterically as they walked around spraying me from every angle (and point blank), but the joke was on them as I emerged fully dry. 
Since that test I have had seven nights of pouring rain (>10mm), and countless others that were (at least) lightly raining over the course of the past five months. In total, the Interstellar Bivy has been used 25 nights without failing.
The above water resistance is great, but there are many bivies that are waterproof but will leave you soaked from the inside. The body gives off at lot of moisture over the course of a night, either through your breath or perspiration. A bivy needs to be able to get that moisture to the outside of the fabric, more so than a tent, otherwise you’ll be left with a wet sleeping bag. I’ve slept in bivies before that I thought were leaking but it was just condensation collecting over my head and dropping onto my face. In a tent that moisture will often roll down an angled tent wall and away from your body/sleeping bag. A bivy doesn’t have the room for that.
The Interstellar has multiple ways of dealing with the moisture. First, the AscentShell membrane is one of, if not the most, breathable membranes that I’ve had the chance to use. One of the reasons I was so excited to test this bivy is that my experience with the Interstellar Jacket (review here) was so impressive. Even under high exertion/high humidity the AscentShell works very well, for both applications. If the weather is nice enough you also have no-see-um bug netting that comes down to almost the waist that allows you to roll the solid fabric out of the way (and a toggle to secure it) for maximum airflow.
I’ve also just thrown this on the ground, almost like a ground sheet, and slept directly on top of it, a la cowboy camp, under ideal weather conditions to maximize the nighttime views.
I guess this section is relative, right. If you are the type of person that brings a two-person tent along for a solo trip then you're gonna find this a little cramped. But my guess is that anyone seriously looking to buy a bivy is looking to lighten their load and footprint already. If so the Interstellar is a very comfortable option. There is more than enough room for an (admittedly) wriggly side sleeper.
I am 6 foot, 175 pounds, and have excess room at the head and feet to get comfortable. There are, however, no pockets to store or organize gear or get it off the floor (not unusual for a bivy to not have any pockets, but it would be useful for the extra ounce or two).
I can become a little claustrophobic in bivies that have fabric that drapes right over the face. The OR has a single Delrin pole to give some breathing room space. It can be left at home to save four ounces, but to me it's more than worth the minimal weight penalty.
There is a slight learning curve in making sure that everything you would normally bring into your tent to keep dry, stays dry outside. You can fit a book, headlamp, phone, etc in with you no problem, but things like boots that people usually keep in their vestibule can’t come in (at least my size 11 boots can’t!). I almost always backpack with a waterproof pack (HMG Summit in the summer, Arc'teryx Arrakis in the winter or on longer trips) so most stuff gets tucked in there, and I’ll bring an extra grocery bag to put over my boots. You can also bring a small tarp to have a fully dry entry/exit plus extra storage area. My RAB Siltarp 1 weighs only 7.5 ounces and gives me an incredibly versatile, configurable shelter when paired with the bivy.
The Interstellar is a side/top entry bivy which I far prefer for ease of entry/exit. It also allows you to keep the interior dry should you need to get in and out in wetter conditions without a bivy.

Hook and loop patches reduce strain on the zippers.



Possibly the best part of a bivy is the ability to roll into camp and be in bed within minutes if you want to. It's as simple as unrolling your sleeping bag. Unpack the bivy, lay it out straight, insert the pole (if you are using it), and stake it out if you are expecting bad weather or, like me, toss and turn. You can be fully set up before the water for your dinner is even boiling. There’s no fiddling to make sure you have a taut pitch. Setup time is a minute, literally, maybe two minutes maximum if you are using the pole and both stakes.

Pretty much all there is to the setup.


There are stake loops on the head and foot end (one on each side) as well as a loop on the chest, so you do have the option of leaving the pole at home and still pulling the fabric off of your face by guying it out to a branch above with some cordage.


One small stake loop on each end


Chest loop for securing the extra fabric when rolled back, or for suspending


Inside toggle


Rolled back for maximum breathability while still remain bug-free


The other huge advantage is pack size. The Interstellar Bivy packs down to roughly the size of a one-litre Nalgene bottle allowing you more pack space for what counts—food (or is that just me?). The poles break down into 12-inch sections and can disappear easily into any side pocket.





Only slightly larger than an UL sleeping pad


A last note: The Interstellar is marketed as a four season bivy. I would add the caveat that it would have to be a mild-winter bivy. When I first received this bivy I set it up in the backyard with my Exped Downmat 7 and -7c (20f) MEC bag. It was certainly a little tight and compressed the bag a little. Anything more than that (either a thicker pad, or bag) and both movement would get uncomfortable, as well as your precious insulation compressed. If your winter involves a little milder temperatures than mentioned, then I would classify it as four-season, however don't be expecting a -20c and thick winter pad to fit.

Conclusion
The Outdoor Research Interstellar Bivy is a great lightweight option which utilizes the highly breathable AscentShell membrane to reduce condensation to non-existence, while still remaining waterproof. It packs down tiny, requires little time to set up and provides adequate space to lounge in. I found the extra zippers/sombrero option to be a little gimicky but don't let that distract you from an otherwise highly successful product.
I have been testing the Interstellar Bivy for the past six months (April to September) in Ontario, Canada. Temperatures have ranged from +3°c to +33°c (° to 91°f). It has been used for 25 nights, ten of which have had heavy rain, predominantly backpacking/hiking in the Carolinian and deciduous forests of Southern Ontario.
Source: received for testing via the Trailspace Review Corps (Sample provided by Outdoor Research for testing and review)

Great review, Jake. It's pretty incredible how far technology has come to allow for such a lightweight bivy to be both breathable and waterproof.
Couldn't agree more, Kiwi! The reason I was interested in testing this in the first place was how successful I found the Interstellar jacket from OR (same fabric, membrane, etc). I usually don't love bivies as so many trap so much moisture (about as much as they keep out), but this one was an exception.
Yes, great review, Jake! Thanks for taking the time to test it out.
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Outdoor Research Interstellar Bivy Review
© Dan Bailey
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Hooped bivvys give you a bit more space and comfort than a simple bag, but less so than a tent. In these days of ultralight single person tents, does the hooped bivvy still offer any advantage? I've often pondered this question - and in this case the answer is yes, in some circumstances. Top model in a new range from Outdoor Research, this excellent hooped bivy (alternative spelling) is as light as some bag-only bivvy bags, and it has a unique feature too: The hooped end can be worn on your head, like a large waterproof sombrero, allowing you to sit up and cook etc whilst remaining inside the bag and protected from rain.
It's designed, say Outdoor Research, for thru-hikers, backpackers and ultralight alpinists. While I'm not sure there's a useful distinction to be made between a backpacker and a thru-hiker in terms of kit requirements (or at all, really) the general theme is obvious - this is a minimalist alternative to a tent that's aimed at all weight conscious mountain travel, whether you're walking or climbing.
I think it's ideal for use in the UK, being arguably a bit better than a conventional bivvy bag in wet weather. It also has obvious application in an alpine setting since it is genuinely light enough, while still offering you a good bit more than a simple sack design. I can certainly see myself using the Interstellar on trips like the Cuillin Traverse.
You're supplied with a bivvy bag and a short collapsible plastic pole. In its stuff sack this weighs just 590g, not a weight that's going to break the bank. By comparison a simple non-hooped bivvy I happen to have here, an old Rab Alpine SL, weighs 416g. The Interstellar is a more spacious bag, and I think that extra 174g is a price worth paying for the additional livability you're getting.
Versus a small single person tent, the Interstellar comfortably beats most mass market models for lightness. At a bearable budget you can expect your one-person tent to weigh around 1kg. Pay a lot more and there are ultralight specials that come in at a similar sort of weight to this bivvy, and in a few cases undercut it. So yes, you can get more space for less weight than the Interstellar. For example, take the new Terra Nova Pulse Ultra 1, billed as the lightest tent in the world at just 490g. Sounds amazing: But this costs around three times as much as the Interstellar, and I'd be willing to bet its fabrics are not half as tough. You'd never take that to the Alps. Overall I think the Interstellar's balance of weight and space is a good one.
Pegs add a fraction to that weight, and you have to supply your own.
With cold hands, in the wind, it's a bit of a struggle to cram into its bag (feet first, to squeeze the air out) and I think a marginally larger and more robust stuff sack would have been good, at the cost of only a few grams to the headline weight. The packed size is a negligible 30cm long - easy enough to squeeze into a compact climbing or trekking pack.
The pole forms the single upright span. At first I found it a bit hard to force into its sleeve around the head end - and you don't want to push too hard since it's only plastic. But things have softened up after repeated use and it now slides in easily enough. It simply velcros into place - there are no eyelets, as you'd find in most tents. Now peg out each end of the bag and you're done; the whole procedure takes seconds.
For added stability in wind you can guy it out at the head end - though no guyline is supplied. While it's not a serious issue I have found that the upright section of the bag can twist a little in use, or lean slightly off the vertical, since the bottom ends of the arch are free to shift about; side pegging points might have stabilised the structure at the head (I'd be tempted to sew my own if I was sure of doing a decent job).
The Interstellar comes in only one size. At 183cm tall I can sleep in it with room to spare, so it's safe to say it's long enough for tall-ish adults. There's plenty of width at the head end too; the experience is not claustrophobic and there's room to wiggle about a bit, and roll over in your sleep. In terms of height, while you won't be sitting upright that hoop does give a bit of headroom and holds the fabric well away from your face so there's less of that enclosed feeling you can get in a non-hooped bivvy. I've found I can read a book inside the bag for instance. With a bit of contorting I could probably change my top layers without emerging. I can also keep a torch, book, bottle and spare clothes at the head end of the bag without losing everything. It's never going to match even a tiny tent for livability, but if I was bag-bound in rainy weather I'd far rather it was in the Interstellar than a non-hooped bivvy.
Mat in, or mat out of the bivvy bag? It's been an open question for as long as both have existed. I tend to favour mat inside, and in this case doing so holds out the sides of the bag and helps maintain its structure and tautness. However this is still a moot question, because while the Interstellar is roomier than many bivvy bags, its internal space is not limitless. Add a thick inflatable mat inside, especially a wide-footed oblong mat, and bag room at the toe end does begin to get tight. This is something I've noticed when trying to lie on my back, when there's simply not enough slack to comfortably accommodate my feet in upright position. Yes I do have massive feet; but I can't help thinking that more of a box shape at the toe would have been an advantage. Failing that I will just have to remember to use a thinner mat, or a tapered model.
Underneath the waterproof layer is a secondary flap made of insect-proof mesh. Although midge season has yet to get underway this will doubtless be extremely welcome over the summer months, making Scottish bivvies if not pleasant then at least humanly bearable. So far I've not needed it, and have simply tucked it down into the bag where it's completely out of the way. We don't have many bone dry nights in the UK, there's always some dew, but if you do want to sleep entirely open to the stars then you can roll the main door down and secure it with a little retainer, leaving just your legs under cover. I imagine that would be lovely on a warm summer night in the deserts or mountains of the US, where this bag was designed.
It's worth mentioning that the zip-around entry is enormous, so unlike a top-opening bivvy bag there's never a struggle to get in and out.
This is really the unique feature of the Interstellar, the obvious thing that sets it apart from other hooped bivvys. A dimple in the fabric at the hoop end is shaped and sized to perfectly fit onto your head. Assuming you're not pegged down, you can sit upright and the head end of the bivvy effectively becomes a wide brimmed hat, with the pole forming the rim. This looks a bit unusual (no points for style) but it works surprisingly well.
The result is that if it's raining (or, in the case of the above picture, very cold and windy) you can sit up and perform close tasks such as cooking without having to leave the shelter of your bag. It's a neat idea, and a solution to a genuine issue since such things are normally a bit of a struggle to achieve in a standard bivvy bag. Nice, too, that you can sit around at a camp and still stay out of the weather; in a standard bivvy you're either lying down snug but entombed, or you're out in the cold.
To facilitate the hands-free aspect of this design, OR have had to add a lot - and I mean a LOT - of zippers. The door flap has six zippers, two for each arm and two for the head/main entry, in addition to which the insect mesh has a further six corresponding zippers. That's a total of twelve zippers, each of which is double sided so that you can use them from inside or outside the bag. Add a large zip pull to every possible point and you're left with a potentially confusing array of dangly bits. It's fine when you can see what you're doing, but despite the addition of glow-in-the-dark zip pulls (a nice touch) it can be hard to know which zipper does what when you're half asleep in the middle of the night and fumbling to get out for a pee. Before retiring you also have to be very careful not to have left an inadvertent opening somewhere, or you'll risk a soaking if it rains.
Despite the plethora of zippy bits I think the whole thing is a success, adding a new degree of usability to the traditional hooped bivvy design. I can see it being particularly good on a cramped alpine bivvy ledge. Sounds cheesy but, like OR says, it really does blur the line between apparel and accommodation.
The top side of the bag is Outdoor Research's proprietary waterproof/breathable AscentShell, a 3-layer, 20 denier nylon membrane fabric. I've not yet bivvied out in prolonged wet weather - even a reviewer has to draw the line somewhere - but so far it's kept me dry in a passing shower and light snowfall. It is fully seam taped, and on paper its hydrostatic head of 15,000mm makes it easily waterproof enough for a night out in heavy rain. I can tell you that the Interstellar certainly passes the back garden hosepipe test.
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