I was looking for a light, Bivy/Bag Cover mainly for emergencies but functional as a bag cover for wet nights out, or in a snow cave/shelter etc...Pros: simple, light, cheap$. Cons: Hard to get into and out of, strange/dorky zipper, not seam sealed, seemed cheaply designed and assembled. I also tried the Mountain Hardwear Conduit SL which was small (I'm 6'/200lb) and heavy. I returned both of them. I got/love/highly recommend the MontBell UL Wide/Long Gore-Tex, seam sealed Bag Cover. Just what I was looking for, and mine weighs in at only 8.25oz including stuff sack.

This item performed terribly for me. I used it on 2 overnight ski tours in the Columbia mountains of BC - both times getting my sleeping bag soaked from condensation. I also used it for an overnight well below the snow line and above freezing temps, and it still filled with condensation. This thing does not breathe at all, regardless of temperature, inside or outside of a tent. It sucks, which is a shame as I am normally a huge fan of Black Diamond gear.

I used this bag in the Lake Tahoe area on a perfectly clear night with temps in the 20's. Unfortunately, my sleeping bag got wet from frost and condensation. It makes me wonder why this bag is called a "winter" bivy when it can't even handle a mild night. Definately not worth the money.

I agree with other reviewers. This thing doesn't breathe. The inside was wet from condensation after 1 night in a snow cave. Talked to an R&D guy for Kiwi company Macpac who tested Epic fabric way before BD used it. The verdict was "not the most breathable fabric around..or the most waterproof ... Ok for N America dry snow but not kiwi wet snow."

This Bivy sack does what it's meant to, nothing more. It is amazingly light and is designed to keep you warm and dry while sleeping mostly ABOVE the snow line. i.e. when it is cold and snowy and rain is not your biggest concern. The biggest advantage is its highly breathable fabric (my experience, I see some controversy here), which is priceless as I use a down sleeping bag. Its disadvantage are the almost "transparent to water" seams, hence I strongly recommend sealing the seams for true water resistant (NOT waterproofness) If your are after water proof, Gore-Tex, and the like, this is not your sack.

I bought this as an emergency bivy for backcountry skiing. It is a great little bag, once I'd consider taking with me on a trek where I might have to do an emergency sleep out overnight. Very small and light, not many extras, no zippers, but certainly a great product for its design, also a nice way to increase sleeping bag warmth rating.

I used this in the North Cascades in February during a snowstorm up 6000ft and it was absolutely horrible. Not waterproof, not windproof, and should NOT be considered a "winter" bivy, let alone a bivy at all. It's thinner than tent material and super light-weight, but that is not always a good thing. Get another bivy, not this one.

Pros: This bivy is light and simple, minimal design.
Cons: Small, tough to get into and out of, poor quality.
I tried the Black dimamond and the Mountain Hardwear Conduit SL, sent them both back and got the Mont Bell UL Gore Tex Wide and Long (8.25 oz including stuff sack). Love the Mont Bell.

The zipper can break and its not waterproof but great for emergencies or nights out in the open when all you need to do is keep off the dew.

Black Diamond Winter Bivy Sack came in super handy in the Backcountry. It added warmth to my bag and kept it dry when the hut had too much condensation. All for 9oz. Very nice.

I'm sure this is a great bivy for minimalists, although there are a couple of items you may want to consider before ordering. All seams are untaped and there are perpendicular seems running across the top of the toe box area (top & bottom) as well as down the sides. The shoulder zipper is not nearly as convenient as a full length side zipper. At 55% humidity @ 55 degrees, it seemed to collect condensation as redily as a Mountain Hardware SL conduit bivy.

I got this sack for a trip to Red Rocks thinking it might come in handy if I went in to the backcountry. Little did I know I would be using it the first night because we were short one tent. It kept me dry and extra toasty even though the outer shell was wet with dew. It also packs insanely small. Darn good sack at an awesome price!

I just returned from using my BD winter bivy sack while cycling through France for 2 weeks and it worked very well. I DID NOT USE A TENT, ONLY THE BIVY SACK. It is very roomy and lightweight!

As with all water resistent, breathable materials, it allows for condensation to form in cool temps when the humidity is high but it dries very quickly. It worked very well in the rain and was easy to get in and out of. I am very pleased with it.

Thank you!

I was looking for something light weight for winter climbing. On a scale from 1 to 5, this winter bivy is definetly a 4++. Extremely light weight, easy to enter and exit and it kept my bag absolutely dry after two nights in snow caves. Nice price too. I can't think of anything more I could ask. Highly recommended.

Backcountry gets a 5.0 for service, I had the bag within 3 days of ordering and I live in Asia. Can't go wrong ordering from these guys.

I highly recommend the Bibler Winter Bivy Sack...it is the ultralight hiker's dream (9 ounces, verfified on my scale)! I broke the bivy in during a hike through the White Mountains, NH in miserable conditions (sleet, snow, freezing rain). Paired with my SilPoncho, I spent the night warm and dry. The bivy did a great job of keeping my bag dry from any splashing rain, but I did find that I had to open the zipper on occasion to relieve some of the condensation. Despite this, I found the Epic shell to be quite breathable (C'mon, I have yet to experience any "waterproof/breathable" piece of gear that didn't have at least a little bit of a condensation issue...so I'm realistic in my expectations). This product gets my highest endorsement for the ultralight hiker.

This is one of the lightest, super compact (size of a soup can) bivy sacks out there on the market and for this price it is a steal. Water resistant, tear resistant and added warmth to any mummy sleep system, it is great for that unexpected downpour or just by itself on those warm summer adventures. A must have for the avid outdoorsman(woman)-- outdoors-person!

Last winter I did a winter camp in yellowstone and my down bag was drenched from the condensation by the end of the week. This past trip I used the Black Diamnod/Bibler winter bivy sack on the outside and a western mountains vapor sack on the inside and my bag remained dry thoughout a week of winter camping.

The winter bivy sack is extremely lightweight and compressable. It keeps your bag dry from mist, moisture and condensation (although I only used it iside the tent, and I'm not sure how much the vapor sack was responsible for the dry bag this year).

The downside: It only has a horizontal zipper accross the upper TOP portion of the bag which can restrict movement/motion. If the zipper extended down the right side (to match my sleeping bag) then it would be a 5 star item!

This is very bare bones but does the job. There's is nothing but the windproof/water-resistant fabric and a very light 2-way zipper across the shoulders. I've used it once so far in 15F dry weather surrounding my 20F sleeping bag at 11,000ft on San Gorgonio. It's so small and light that you can pack it anywhere and it makes a good conversation piece.

This bivy packs up small enough to put in a pocket! Condensation wasn't a problem for me when I used it, but it was dry. It's just a handy thing to have around because it takes up so little space and does exactly what it was designed to do nothing more and nothing less.

When I summited Denali, I had this lightweight gem in my pack. I also use it to extend the warmth of my 900-fill TNF 15-degree bag. Very versatile!

Used the bivvy bag with a PHD bag in Austria at minus 26C and it performed brilliantly. The bag is VERY light, but still surprisingly strong. You may need to pop a bit of string onto the Zip puller to operate with gloves, but otherwise a very good bit of kit.

The weight and compression are great. I used it in heavy rain, it helps about as much as it weighs…zero. Not that it is designed for that anyway. Otherwise it does a fantastic job of blocking morning dew and snow won’t stick to it either. It’s excellent when used with a shelter, I'm able to use my down bag more often thanks to this! The tiny zipper is a pain with cold/wet hands, and the material has a "static cling" effect when damp. Great for the minimalists! BD has great customer service too.

Used for winter camping in -10 to 20F.

Pros:
-Excellent, light protection from elements for bag.
-Above-average breathable.

Cons:
-Single zipper across shoulders is challenging for inserting pad and bag(s), especially when freezing (no side zip).
-No face panel; zipper slit not ideal for external visibility or ventilation.

I spend 6 months a year sleeping under the stars. I don't like tents. I use to freeze in my sleeping bag in the spring and fall months. When I got the winter bivy sack, it added the extra 10-15 degrees I needed to stay warm without a tent. Just by blocking out most of the wind, that a tent would do. It is small and very light weight.