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.
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.
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.
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.
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.
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.
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.
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.
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.
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