Montbell Bivy Experience?

I had the gore-tex one but never used it, so can't comment on the performance. I can say that the bivy is quite narrow at the footbox and is spartan in the middle too.

My wife uses a full length prolite 3 pad and 20* bag which was tight inside the equinox and montbell bivies. Torso pad and quilt would fit ok, but I thought overall it was too narrow. I'm 5' 8" and 150 lb.

The opening is very large and is mummy type with drawstring. No zipper.

I've seen them.They really are bag covers rather than full-fledged bivys, what with the small size, rudimentary closure and hood, no provision for netting. Everything but the size could be hacked, I suppose, but Montbell designed these as covers, not bivys—-and that's what MB calls them. It would be hard to see using them outside a tent or tarp environment. A lofty bag could be constrained inside one of these. The Dry-Tec model is the far more interesting one in terms of price and breathability.

I use one as a sole shelter on solo trips and when racing. I turn over in the rain or put my jacket over the opening. It's super duper minimal. No venting and only the drawstring closure. Cheap by SUL bivy standards. It's probably not for most people but it packs tiny, keeps me dry and works perfectly with a short quilt/jacket setup. Don't have any bug issues a headnet doesn't solve. I use it without a groundsheet and it's held up fine so far.

I'm sure if you search my posts I wrote more about it too somewhere.

Yes, Christopher, but like we Alpinists, you Adventure Racers are nuts. :-D>
I salute your adaptability. Incidentally, do you use the Dry-Tec or GT version?

Chris, which Montbell bivy do you have? Did you get the long version?

I bought one earlier this year. Mine was the Breeze-Tec UL cover. Weighed in at 6 ounces on my postal scale. Not bad for a waterproof breathable bivy at $110. I used it as a sleeping bag cover – meaning I didn't try to put the pad inside. Everything about it was perfect, except for the breathability.

Here's what happened: I wake up in the night. The air is still, it's cold, maybe right around freezing. The stars are amazing. I am really happy to be sleeping out here in the open. I pull my hands out of the bivy and touch the outside surface, its wet, covered in dew. So is my pack next to me. No problem I'm thinking, this is a waterproof bivy. Indeed it is. But as a touch my sleeping bag my heart sinks. Its wet also. Luckily it hasn't soaked the down yet, but the shell is pretty damp. I eventually go back to sleep.
The next morning I dry out my sleeping bag in the sun before I pack up. Maybe this is how all bivies are, I don't know, but I'm dissapointed.

I returned the bivy.

I was initially apprehensive about size due to the country of origin, but the dimensions listed seem to be generous enough compared to other ones I've used. They have a wide and long version too.

I currently use an eVENT bivy. I set up a poncho-tarp over the head end in wet weather so I can vent it better, and as a place to keep gear dry. But my eVENT bivy is heavy at 19 ounces, and overkill for predicted dry weather.

So, to go lighter, I am either going to need a DWR bivy/bagcover with top made of Pertex Quantum or similar, or a light WPB like the Dry-Tec. Given the breathability numbers of the Dry-Tec, I thought it might be more consistent with my preferred use.

ADD: Kristin, depending on humidity I think you'll find most bivies perform similarly to your experience if used out in the open. I've been damp inside my eVENT bivy before, but it's rarer than with any other I know of (the eVENT covers a broader range of temp and humidity than most fabrics).

Yes I know I'm nuts :) I have the regular length 6.3oz Breeze tec UL model. It is *just* barely big enough for my 5'11", 155lbs, esp in length. My winter bag (-25) does not fit in it. I put my closed cell foam pad (3/8" blue or 1/8" thinlight depending on my desire to cut every ounce) and my pack under it as ground sheets.

Seriously if I was hiking for months and wanted to be more comfortable I would SO rather have a poncho tarp and a SUL bivy combo. It would breathe better and let you hide out in foul weather more. On a couples trip with my wife I'm not going to get away without a full enclosed tarptent or singlewall tent. So solo I go spartan, sleep a minimal amount and enjoy that type of adventure. If I'm going to carry more weight I think I'd rather have a BD Firstlight or TT Contrail.

But for what I use it for it's fine and I have found no better option save a custom WP/B and Cuben bivy. I stay dry, it breathes well enough for a bivy (far better than AMR thermolite bivys), packs tiny and requires nothing more than rolling it out and crawling in (no stakes etc). My quilt usually stays inside and I'm often wearing my jacket already from cooking dinner or chilling from being wet and tired. I'm very happy with the product but it has it's niche.

Kristin, I have the MB bivy cover, goretex version, W/Long, and a down bag also long. I believe what happened to you that cool night was that the water vapor moving through your sleeping bag cooled to the dewpoint when it exited the outer shell of your sleeping bag (still inside the bivy). It then condensed to liquid. The same thing will happen inside a goretex shell bivy. EVENT might allow the moisture to continue moving outwards faster than it can cool (not sure).

So your bivy's Waterproof/Breathable material can not transport liquid moisture unless it is condensed on its inner surface.
The only way to minimize this situation, with Drytech, or goretex, is to not breathe down into the bag. Keep your head, or at least face, outside the drawstring. This works for me with a that goretex cover and my MB down bag.
Sorry if you already knew all this.. Another solution is use a synthetic bag in humid/wet environments. It retains loft and dries literally in minutes in sunshine.

You don't want to be breathing down a eVENT bivy, either. A wonder fabric, perhaps, but not a laws of physics breaking wonder fabric. As Brett says, keep mouth and nose exposed to opening. Also, even a synthetic bag will lose some loft when wet—you still need to retain good discipline in keeping moisture sources at bay. The saving grace of synthetic insulation is that it will retain some loft and will dry out much more rapidly than down. Those of us who use down in prolonged wet weather or during a long Winter's trip will use any break in the weather as an excuse to drape the bag outside to try to dry it out. One can be more casual with a synthetic bag.

Thanks for your replies guys. Yes, I think I knew all this, at least theoretically.

This particular bivy saves weight by being a very simple design. No poles or guyout points and no zippers. That design also aggravates the condensation problem by not having any possibilities for venting nor any tools to keep the wet fabric away from the sleeping bag.