MSR AC Bivy review in the snow

MSR AC Bivy Review – Updated

It’s time for me to update my MSR AC Bivy review. I’ve spent quite a few nights in this yellow cocoon and have formed some new opinions on it.

MSR AC Bivy Review

The MSR AC Bivy is generously sized, it’s the kind of bivy you can place a full-sized ground mat, a large sleeping bag and a daypack into and still have room to shuffle, it opens from the top with the zip going straight across the width of the upper side at about eye level. I’m only a mere 5ft10 or so but this bivy would be fine for people bigger than me as the pictures hopefully show.

MSR AC Bivy review in the snow
MSR AC Bivy in the snow

The bivy’s shape tapers towards the bottom to reduce it’s size and weight but the top remains quite wide so there is enough volume around the shoulders to fold your arms under your head if you sleep well that way.

The MSR AC Bivy is unsupported so there are no poles or beams, the material of the shelter just lies flat when you’re inside. There is a small material loop in the center on the top edge of the hood so you could attach some para cord or rope and hold it up if you wanted to but the material is very light and I don’t find it irritating at all. At least not until it rains which I’ll discuss further down.

MSR AC Bivy Review
MSR AC Bivy in stuff sack

The MSR AC Bivy packs down into a very small stuff sack that measures an actual 20cm by 10cm just as MSR promise. It has to be said that the stuff sack is a pretty tight fit and it can be a pain to re-pack in bad weather, even for meticulous and seasoned folders and packers of bivys and tents. Because of this I sometimes keep mine in a slightly roomier 2L roll top drybag (which it doesn’t fill).

Keeping the bivy less compacted I believe will also prolong it’s life because there will be less tight folds in the material, this can cause some wear especially if the bivy is folded and packed the same way every time.

MSR AC Bivy Review
AC Bivy – grippy bottom surface

Some technical details; the MSR AC bivy is fully waterproof and uses taped seams and although MSR state the fabric is breathable they don’t specify any numbers.

At 510g the MSR AC Bivy’s pack weight puts it in the very light to ultra light category without it being an emergency only bivy. This shelter is certainly fit for multiple consecutive nights and long-term use. It’s a little over 2.24m long and 0.91m at its widest point, which is the head area. The ground material on the inside feels grippy which helps to stop ground mats from sliding around inside.

MSR AC Bivy Review
AC Bivy – mosquito net

Now lets talk about something I feel very strongly about – the mosquito net. This is how I see it – I don’t like it when mosquitos chew on my face, therefore mosquito nets in bivvies are absolutely essential.

Thankfully the MSR AC Bivy has a mosquito net, what’s more, it’s a pretty fine one too. It’s made from a dark material which makes it really easy to see through, because there is no scattered light from the material. It’s also large and has quite good zips.

I like to be able to see through the net, it’s part of what makes bivys quite social and also means you can stargaze at night when the insects are out and generally check out your surroundings. I also find it helps to make them feel more open and less claustrophobic.

MSR AC Bivy with Alpkit Airo 120
MSR AC Bivy with Alpkit Airo 120

The MSR AC Bivy is my go-to bivy of choice for cycle-touring, fast and light hikes and pretty much every tent free adventure. It’s breathable and performs well up to warm temperatures, with a gentle breeze it stays bone dry inside and has a great mosquito net.

MSR AC Bivy Review
MSR AC – taped seams on inside

So far I’ve tested The MSR AC Bivy in these weather conditions:

Howling wind: It flapped a little due to it’s size and the hood has no fastening mechanism, in strong gusts the hood would occasionally blow up as far as the mosquito net would allow. If it also rained then it would become necessary to fasten the hood down, perhaps with the little tab/loop of material on edge of the hood. During the night I reoriented myself so that the head of the bivy was facing the wind which helped to keep it closed.

Cold and damp with light rain: Performed brilliantly, stayed dry even with the hood fully closed and the moisture from my breath going inside.

Cold and dry with slight breeze: This is perhaps the easiest conditions for any bivy so again I had a sound nights sleep. Any shelter of this quality wouldn’t bat an eyelid in those conditions anyway.

Consecutive nights of warm with heavy rain: This is a difficult environment for bivvies, their breathability often suffers. The MSR AC Bivy is no exception but it was constantly fighting to keep me dry and I was comfortable despite some damp accumulating around my feet and around my nose and mouth.

It was the consecutive nights that the MSR AC Bivy found most difficult, my down sleeping bag didn’t really dry out and got slightly damper each night. From this experience I can say that I would not want to camp in more than 4 days of rain.

MSR AC Bivy Review
close up of the materials

My overall verdict is that The MSR AC Bivy is fantastic for it’s price; it’s spacious, waterproof with well taped seams, the material feels strong and packs down surprisingly well considering the high volume of the shelter. I personally use the bivy on top of a small tarp to stop snags and scrapes damaging the underside as I do with all of my shelters, tents included, but I’d have no reservations about using it by itself on grass or other soft ground.

inside the AC Bivy
getting adjusted

MSR AC Bivy review update:

I’ve now tested the bivy in freezing temperatures in the snow after a long and sweaty hike: even getting into the bivy damp I was warm and had dried out by morning.

When packing up I noticed some condensation had ended up underneath my ground-mat but it didn’t affect my nights sleep and was likely due to me being very damp on entering the bivy. I was very happy with the performance, it even coped with clumps of snow melting off the trees and landing on me during the night.

If you found this MSR AC Bivy review useful please consider sharing it or leave me a comment below.

13 thoughts on “MSR AC Bivy Review – Updated”

  1. Hi James,

    Nice review, actually one of the few MSR AC bivy reviews out there. I’m interested about the opening. You write that the bivy closes with a zip across, but I understand from other reviews that the zip actually closes the bug mesh and keeps the bivy open in a sort of envelope style. One reviewer mentioned that this opening created a funnel that led rainwater straight into the bag…
    Can you shed some light on this? I love the weight and size of the bivy but I’d like to stay dry, even without a tarp.

    1. Hi Robert,

      Yes you’re quite right the bivy’s zip actually only closes the netting and although the opening folds closed it’s not held shut by anything. I think sleeping in a bivy might be a matter of technique. If you closed any bivy all the way you would soon be wallowing in your own perspiration in most weather conditions.

      When it’s raining the best course of action (in my opinion) is to roll over so that the opening is facing down. That way you have fresh air, an exhaust for respiration and hopefully a good dry nights sleep.

      If you place your bivy over your ground mat, rather than placing the mat inside the bivy, you’re much more able to move, curl up and position yourself so that you stay comfortable and dry.

      Thanks for your question Rob, I hope that helps!

  2. Wow thanks. If it only were lighter. I am searching for a bivybag that’s as breathable as this, without necessarily being waterproof – water resistant would be enough, because I’d use it along with a tarp over my head to keep most of the water out. Do you have any reccomendations? Thanks :)

        1. Sorry Fabio, I’d just woke up when I answered your question and clearly wasn’t at my best!

          If you’re using a tarp over the top of your bivy then you might be best investing into having a full tarp and not using a bivy at all. I have camped out under a small tarp with no bivy in the rain and (apart from the occasional splash from raindrops) been dry and comfortable.

          The only downside is that you need to get a pitch for your tarp – trees, walking poles, bikes are good structures and then you’ll need a length of paracord too.

          If you’re set on the bivy option then the Alpkit Hunka is quite light and breathable. It’s also very cheap, though it’s sometimes out of stock (like now):

          One last thought, have you considered using a silk liner as a protective cover. I use one on the inside so that I don’t have to wash my sleeping bag quite so often. It might just work on the outside to, especially if you treat it with Nikwax, etc?

          That and a full tarp might be an elegant, light and breathable solution. Good luck Fabio! :)

  3. Hi, what size/weight of tarp do you use under your bivy? When I think tarp i think of a massive heavy bit of woven polyethylene.

    1. Hi Jackson. That’s a good point, normal tarps are really thick and heavy and are not fully waterproof. I use silnylon which is quite light and extremely thin and practically aquaphobic – the water just can’t wait to get off it! It can be bought pretty cheap from Amazon in square sheets of various sizes. Do you use a bivy?

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