Outdoor Research Interstellar Bivy Review: Tiny Home Between the Stars

The Interstellar Bivy from Outdoor Research sets out to hit a sweet spot between lightness, protection, and usability – with a “wearable” approach to what a bivy can be.

The bivy caught my eye when OR showed it at the OutDoor trade fair in the summer of 2018 already.

After all, if you want to travel light and fast over trails, you won’t want to burden yourself with an outright tent. A bivy, small and light as it can pack, can have a hard time proving its mettle over a mere emergency bag and against a tent offering room to get camp chores done, though.

The Outdoor Research Interstellar Bivy slots right in between…

Full disclosure: I received the Interstellar Bivy I have been testing from Outdoor Research, for free, without obligations to review it, let alone any influence on my editorial reporting.

A Mountain Overnighter's Morning View
A Mountain Overnighter’s Morning View

Why Change a Bivy?

The Helium Bivy from Outdoor Research has already led me to many an interesting experience and served me well.

I liked it well enough, and not only because I had also received that bivy for free to review it if and as I saw fit. Rather, it is light and useful. But, it also has some issues which I didn’t hold back on.

The Interstellar Bivy was built on the feedback of Outdoor Research users – and it shows.

There are still some things to know and consider – and I have only had it since late 2018, i.e. for a few months of fall and winter. Thus, I will still need to add hot-weather experiences to this review (or write a part 2).

That said, I can definitely give first impressions, based as always in my reviews on my own actual use, for the Interstellar Bivy. And with a few caveats, I have come to love this little Interstellar outdoors home.

First Impressions

For a bivy that is no longer preferably just for warmer weather (3 seasons, like the Helium Bivy), the 4-season Outdoor Research Interstellar Bivy first surprises with its size and weight.

Packed, it takes up a little bit more volume than the Helium and weighs a touch more, but the difference is barely noticeable:

Where the (old*) Helium Bivy, made of Pertex Shield+, weighs 18 ounces (510 grams), the Interstellar, made of AscentShell material, weighs 19.9 ounces (564 grams).

Both bivies’ weights given here include the single Delrin pole they come with (which weighs some 50 grams on its own).

[*There is actually an updated version of the Helium bivy out now, which weighs only just over 1 lb. (16.8 ounces) or 476 grams.]

OR Helium Bivy vs. Interstellar Bivy, In Packing Bags
OR Helium Bivy vs. Interstellar Bivy, In Packing Bags
OR Interstellar Bivy vs. Therm-a-rest NEOAir mattress
OR Interstellar Bivy vs. Therm-a-rest NEOAir mattress… which hints at the mattress being a bit of an issue already…

On the first setup, it becomes clear that the Interstellar Bivy will take a little getting used to, but the issues that give that impression are also the elements which increase its usefulness immensely…

How the Interstellar Bivy Sets Up and Stands

Threading the pole through its loop is, at least at first, a bit harder than it was on the Helium Bivy. That happens because the material forming that loop is harder, and for a good reason:

On the Interstellar Bivy, loop and bivy entrance are moved quite a bit, so that the pole/loop sit right above one’s head and form the very end of the bivy (naturally, given that they are above one’s head).

OR Interstellar Bivy with Mosquito Net Closed
OR Interstellar Bivy with Mosquito Net Closed

The entrance is no longer at the top part of the bivy (where it remains on old and new Helium Bivy models), “above” the pole/loop, but in the upper third of the bivy’s body.

Consequently, the Interstellar has even less of a tent-like silhouette than the Helium. Rather, it has just become a shell for one’s sleeping mattress and bag – and all the better for it.

Once a sleeping mattress – let alone, a sleeper – is inside the bivy, the Interstellar now stands very well.

No longer does the pole’s loop tumble so that the bivy’s cover and/or mosquito netting end up against one’s face; it nicely keeps the cover up and at a distance.

Interstellar Gazing Options

The way one can now enter/exit and close up the Interstellar bivy (just like its sibling, the Stargazer) is to open it at the top or towards the sides; the zippers reach around so far that the whole upper third of it can be opened up.

This sounds and looks a bit as if rain could just fall in, unlike on the Helium Bivy where the top parts (almost) always fall so that the bivy is closed, but it actually makes for enhancements.

For one, far as the zips go, it is also possible to get in from the side, if one wants to keep precipitation out.

More importantly, this configuration makes it possible to zip open the AscentShell outer material, roll it up and hook it down so only the sides of it will flap in the wind (and if there were so much wind, you wouldn’t open it so wide), lie under the no-see-um mosquito netting alone.

Hook and loop in the middle, to tie down the cover if opened up completely
Hook and loop in the middle, to tie down the cover if opened up completely

Let the mosquitoes buzz safely at a distance from your face – and kept away by the pole/loop of the bivy – while you gaze at the starry night sky above you.

Exactly what I love bivies for.

Bad Weather Use and the Interstellar’s “Wearability”

I have not had experiences using the Interstellar in more than snow, let alone needing to do camp chores in inclement weather, but it has a peculiar trick for that:

The Interstellar Bivy gives a new meaning to the word wearable. It’s not an app, not any electronic device, but a bivy that you can, to some extent, wear.

Moving with my bivy...
Moving with my bivy…

Top Weatherproofing’s in the Details

First of all, though, let me mention just how nicely the cover’s zippers are protected.

The stronger material forming the loop already extends to cover the zippers. Then, just underneath them (towards the foot of the bivy), the cover material folds back on itself. And towards the bottom of the loop, that material folds around again to cover the zippers…

Loop cover and fold at the top
Loop cover and fold at the top
Cover and fold-back at the bottom
Cover and fold-back at the bottom

In effect, water that flows down from the loop will just flow onto the cover material. Water on that upper is still being held back from the zippers, even if wind were to push it towards them. And water flowing down the sides just flows down the AscentShell material protecting the zippers.

This is just the kind of small details and attention paid to them that I really enjoy seeing in outdoors gear.

AscentShell Performance

The AscentShell material – also seen in the Interstellar Jacket from Outdoor Research, for example – really does seem to hold its own.

Waterproofing and Breathability

The AscentShell has no issues with precipitation (at least, any I’ve encountered so far; we’ll see about downpours), and it is obviously nicely breathable.

I can tell, first of all, simply from rolling up the bivy.

Where the Helium needs to be rolled up from the foot to the slightly opened top in order to blow all the air out, the Interstellar can be rolled up from top to foot.

The air just escapes right through the AscentShell membrane, which it doesn’t do from the Pertex Shield+.

Close and Cover – and Breathe

The great breathability is also noticeable when closing the bivy – and this is a bivy made for 3-4 season use, i.e. also for the winter:

As much as I liked the Helium bivy already, it was absolutely necessary to keep it slightly open to avoid a feeling of being suffocated, not getting quite enough air.

In the Interstellar bivy, I have not had that issue at all.

I shut it against the freezing nights, and there was no issue with breathability at all.

There was only a slight bit of ice having formed right above my mouth and drifting down in the morning, as I opened the bivy back up, but that was it – and it was gone within minutes, if that.

Nowhere (else) did I notice any condensation, ice, or anything (and I had most of the things you can see around the bivy in the video inside the bivy, outside my sleeping bag, during the night).

Hood the Bivy Up

The second part of the Interstellar bivy’s protective nature is where it all becomes “wearable” – and a tad complicated:

The Head Bump

There is a “bump” in the head part of the bivy, where one can put – big surprise! – one’s head in order to “wear” what is otherwise the head(board) of the bivy like a hat.

That makes the whole top like a hood or wide-brimmed hat, kept in shape by the loop that otherwise keeps the top (i.e., the top when one is lying in the bivy) away from one’s face.

The 'bump' for the head, as seen from the outside...
The ‘bump’ for the head, as seen from the outside…
... and the Interstellar Bivy top, when "worn" right...
… and the Interstellar Bivy top, when “worn” right…
... and when it all doesn't want to work the way it should.
… and when it all doesn’t want to work the way it should.

Does it Stay Up?

The slight problem with this is that, when wearing a cap or trying to be in one’s sleeping bag as well, and especially with a winter sleeping mattress in the bivy, it will all try to fall back into a supine position.

In the end, then, one only holds up the bivy with one’s forehead pushing against the bivy’s loop.

This may also, at least in part, be a result of how the bivy is made to be relatively snug, so that thicker winter gear fills it close to the brim.

It is a somewhat odd mixture as there is room for putting e.g. one’s shoes and some sensitive gear into the bivy. And, not least thanks to the loop, it does not feel claustrophobic. It still is a bivy, and one that is supposed to be “wearable”, though, and not a tent.

Head zipper pulls, when all is closed. Close, but far enough away
Head zipper pulls, when all is closed. Close, but far enough away

Only having one’s head in that bump, without a cap, and with a lighter sleeping mattress and bag, it all works/wears considerably better – but then, it may be less necessary.

The Head and Arms Zippers

For both the outer cover and the mosquito netting, there are zipper pulls for both arms and for the head. With those, one can open the bivy up selectively – which leads us to the second part of its “wearability.”

In situations with lots of mosquitoes, for example, keep your face behind the mosquito net, leave the protective cover open, and only put your arms out to take care of your cooking.

Or, keep the outer cover closed as far as possible, except for an eye slit and arms outside for camp chores whenever necessary, if there is a lot of precipitation you want to be protected from.

This is all useful and interesting, but it also makes for three sets of double zipper pulls (for head, left and right arms) each on the mosquito net and the protective outer cover.

A few many zipper pulls, when all is opened
A few many zipper pulls, when all is opened

Advice: Watch Your Zippers!

Some organizational care is highly recommendable, therefore:

Make sure you have the zippers where they should be; the ones for the arms down the sides, the ones for the head at the top.

Or perhaps, slide the mosquito net’s “head” zippers as far down as you want them, to make it easier to just get in or out through the outer cover – in which case, your mattress and sleeping bag can get caught up on the mosquito net when you are at the point during the bivy’s setup where you want to push those in…

Like I said, good and useful ideas which also make for some issues to learn to deal with appropriately.

Interstellar Stargazer

I have not, of course, made it to warm-weather bivouacking yet (as the bivy has only just been released in the winter of 2019, and even I only got it a bit earlier that winter).

Like the more-simply constructed Stargazer bivy (which lacks the “wearability” of the Interstellar), the Interstellar bivy promises to be great for that, though:

Open up the cover and hook it in so it doesn’t flap around – if the hook and loop you find there are really made for that; they are a bit of a tight fit for that use.

Close down only the mosquito net and you’ll not be seen too much, the netting will be safely away from your face, and you can have a wide field of view into the starry sky above…

Dark Interstellar Bivy in "Storm" colorway disappearing into landscape
And the Interstellar Bivy in the “Storm” colorway disappears nicely into landscapes, too

Great Expectations

The seemingly heavier material made me wonder a bit if I would really be bringing the Interstellar Bivy (rather than my old Helium Bivy) with me in the summer.

After the experiences I have had with it so far, however, I am sure I will.

It will likely be a pleasure for stargazing on warm summer nights, and I will want to see how the material performs in warm (and humid) conditions.

Downpours will also be something where I’d like to see how the “wearability” of the Interstellar Bivy comes into play then, when I don’t have a heavy winter sleeping mattress restricting mobility…

Recently, light tents have tempted me a bit, but my fastpacking overnighters will probably see me out with the Interstellar – and fine with it.


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  1. Toure Weaver

    Im trying to decide between the Stargazer and the Interstellar. Seems like the Interstellar can be a pain with all the zippers. The main reason I was thinking of Interstellar was because it says “4 season”. Is there a difference in the material?

    • From all the info I have (not practical experience with the Stargazer, mind you), there’s no difference in the material. The thinking seems to be that the Interstellar is a bit flatter and offers that “wearability” that makes it potentially more useful in worse weather.
      The Stargazer has 3 inches more headroom, but if you have to do camp chores outside, you have to do them completely outside.

      As for the zippers: Definitely something to get used to; I can understand why some people complain. That said, in general use, I find myself just moving the zippers for the arms to the ends of the zippers’ sides, there in case I need them, and use the “head” zippers for all the normal opening/closing…

  2. Nathan Wheelhouse

    Great review, thanks. Are there any issues with room with your inflatable matress, as you kind of alluded to? Wondered how it compared to the Helium for foot width?

    • Yeah, with the winter mattress (NeoAir SV, regular width), things got quite tight in the foot. No problem for sleeping in it, but tight.

      I hadn’t yet tried that mattress in the old Helium; will do if I don’t forget!

  3. Yvan

    With its mummy shape, it does not look like a large NeoAir XTherm Max would fit inside, but would a NeoAir XTherm large (25″ at the shoulder but narrower foot) mummy shaped fit?

    • Yeah, what I used now was a NeoAir SV in regular, and it’s already tight in the foot. Both width and height might be a bit of an issue; it gets filled up at the foot, but a mattress with a mummy shape should work alright. We don’t get into bivies for luxurious space, do we? ;)

  4. Rick

    Nice review, thanks. Concerning condensation, do you think using it with a down sleeping bag would be an issue? I generally largely prefer down bags.

    • I did use it with my down bag, and it seemed okay… but I really need to get to more time outside with it. Was hoping for some overnighters in China, but the way things went, the bivy is now in China, I’m back in Europe :/

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