The Bottom Line: Outdoor Research Advanced Bivy is the market leader for bivy sacks in North America. Tested on cold alpine climbs and summer trips with temperatures ranging from -10 degrees to 21 degrees Celsius in the Coast Range mountains of the Pacific Northwest, the Advanced Bivy's performance is superb, reliable, and burly.
Bivy bags aren’t for everyone. There are challenges, as with all bivy bags. They are not the most comfortable way to sleep. Getting in and out in the rain is rather awkward, and it is near-impossible to keep all moisture out. (Having a tarp corrects this, but this adds weight to the point a proper tent might be a better option.)
That said, they are light in pack size and weight for solo hiking or lightweight missions, particularly if weather is looking good. Bivy bags are great if you are planning on fast and light alpine missions where sleeping on tiny ledges is needed, you’re a solo-mission gram-counter looking for bug protection, or you need a bomber emergency shelter. If you don’t want to take your chances, and you’d rather not haul a full tent, then the Advanced Bivy is an ideal option.
Setting the Advanced Bivy up is pretty straightforward. It comes with two flyweight poles, one inside, the other outside, that give it shape. For best results, use the stakes; they provide a cleaner, straighter look, and they keep head upright. It takes no more than 10 minutes to set up. Be aware that the pole sets are slightly different in length, so measure them before build. Also, the bottom clasps have fragile necks, so be cautious as you place them.
The Advanced Bivy is fairly easy to get into, thanks to a big hoop enclosure. The zipper closes from the inside, and the mosquito net is optional. For myself, at 5’11, I find it incredibly spacious. I can easily get a 40-liter bag inside with my gear without feeling claustrophobic, even with a wide sleeping pad.
Breathability has never been an issue. Even on an incredibly warm night, with the mosquito net allowing for the mouth to be open, it was a very comfortable setup. Fully enclosed, there is some condensation, but even at warm temperatures less then expected—not enough for any droplets to form, though enough to make the outside of the bag just the tiniest bit damp.
Its waterproofing is terrific. The floor is bombproof, and the material sheds water wonderfully. I never had any leakage issues. With that said, shake it out. If water pools, it worsens condensation.
The Advanced Bivy packs well, smaller than any tent, though the weight is surprisingly high. You won't save any space or weight if you split the weight of a two-person tent with a partner.
The Advanced Bivy is made of a burlier material built to last, certainly tougher then the OR Helium and many ultralight tents. This is one area where it may be appealing for gram-counters not looking to compromise durability at a reasonable price.