I invested in a winter bivy sack this year because I wanted to be able to use it for camping under a shaped tarp or in snow shelters, as a lighter weight alternative to my Black Diamond FirstLight winter tent. I also do more day hikes in winter than overnight backpacking trips, and I wanted a lightweight shelter to bring along for emergency use, in case I have an unexpected night out.
The difference between 3 season bivies and winter ones really comes down to size. For a winter bivy, you need extra girth and length to hold a sub-zero sleeping bag, without compressing its loft and reducing its ability to hold your body heat. Winter bivies should also be a little more resistant to puncture, particularly for use in snow shelters, and to help retain more warmth..
Earlier in the year, I made a decision to buy a Alpine Bivy from Mountain Laurel Designs, since renamed the eVent Soul Bivy, for winter use. MLD also makes my 3 season bivy sack, the Superlight, which is an awesome product, and was a huge success for me last year. So, it might come as a surprise to many of you that I bought an Integral Designs Micro Bivy, instead.
Honestly, I changed my tune because of price. While almost 50% heavier, the Micro Bivy cost half of what I would have had to pay for the MLD Alpine Bivy. Except for weight (18.5 oz vs. 12.75 oz), the two products are almost identical to one another, except that the MLD bivy has a side zipper. In the end, I just couldn’t cost justify paying over $30 per ounce, for the lighter weight but more expensive product, so I bought the ID Micro Bivy instead.
Functionally, the Micro Bivy has a 3 layer eVent top and a 70 denier nylon base, almost identical to eVent Soul Bivy from MLD, but without a zipper. While a zipper would make peeing at night a bit more convenient, there’s enough slack fabric in the hood of the Micro that I can scootch my butt up into it from my sleeping bag and hit my pee bottle without any issues.
This might sound like a private concern, but in winter it helps to hydrate all night long to make up for the fact that you can’t drink enough water during the day. You can’t stop to melt more snow when hiking without getting chilled and you can’t carry a full day’s supply because it’s too heavy.
Micro Bivy Dimensions
So far, I’ve used the Micro Bivy on two nights under a shaped tarp and I expect to use it in a snow shelter by the end of this winter. It’s large enough to contain an inflatable down pad and a -25 degree sleeping bag without compressing the loft. It’s 88 inches long, with a tapered torso (72″ in chest, 64″ in hip, 58″ in foot.)
Construction wise, the Micro Bivy Sack is built like a tank. All of the seams are factory taped and the stitching is tight. The hood has a slight peak on top and has an elastic cord running around its circumference, with cord locks over the shoulders to close the sack off from the elements. In practice, I’ve found it a little difficult to pull closed, but in a worst case scenario, such as a blizzard or driving rain, the Micro is long enough that you can scrunch down it’s length (88 inches) and fold over the door area for additional protection.
I have experienced minor condensation on the top of my sleeping bag when using the Micro, but it froze on the surface of my sleeping bag and I was able to shake it off the next morning without the liner getting wet. Truth is, I was experimenting that night with chemical warmers and I got too hot in my sleeping bag. My guess is that the sweat condensed and froze before it could breath through the bivy’s eVent top.
The next night I slept without a chemical warmer and didn’t experience any condensation, despite the fact that more snow fell that evening. Honestly, I’m not that worried about condensation in the Micro, especially since I only plan to use it in winter when normal nighttime temperatures range from the single digits to 15 below zero (F). Crazy, huh?
This may change when I use the bivy in snow shelters that are warmer and have a potentially more humid micro-climate. It will be interesting to see what happens then and whether the eVent top is really required, or whether the condensation will continue to freeze on the top of the sleeping bag as before.
For me, being able to buy a winter bivy sack off the shelf, with an eVent top, for $187.50, has been key. So far, the Integral Designs Micro Bivy Sack is perfectly adequate for my needs and I expect it to perform well on winter trips for years to come.
However, what was striking about this purchase was the fact that I bought a heavier product over a lighter one, based on price. I haven’t done that for a long time. However, I’m also at the point in my winter gear list, where the only way to pull out a few more pounds is to buy it down, replacing gear with functionally equivalent, but lighter materials.
Truth is, my winter backpacking/mountaineering gear list is hovering around 28 lbs, which I consider to be pretty good, and I’m not ready to spend much more to buy its weight down until I wear out some gear and need to replace it.
Disclosure: The author owns this product and purchased it using their own funds.