icb12,
Which MSR bivy do you have? Your experiences with eVent vs Gore-tex just run sooooo counter to mine and most of my friends that I'd like to check out the specs. I couldn't find one they made in eVent, but did find the MSR E-Bivy, which looks to be a non-breathable supplement/emergency style bivy.
Oak,
If you're OR Alpine Bivy is like the current production ones, it used Gore-tex Respiration Positive, which is a membrane I have no personal experience with. Based on some research, it sounds like an air permeable membrane (which is eVent's trump card) so it is possible that it would perform in the same range as an eVent bivy. Without numbers and better yet experience I'm speculating.
With my Big Agnes bivy, I've had minimal condensation under most conditions (a little might be there, but it's not an issue), except for one very wet trip where the snow was falling fast enough I couldn't hardly keep it off the surface, and there was lots of water inside from my own carelessness. It is definitely superior to my Bibler Hooped bivy, which uses Todd-tex, which should still best standard Gore-tex.
Now if you are going to use a bivy in conjunction with a tarp, in most moderately dry western climates I'd look at a more minimal bivy than anything discussed thus far. My personal choice is the Rab Ultra Bivy, a sleeping bag cover style (as in, it is cut to fit your sleeping bag, you, and nothing else) made of very breathable (even vs eVent) Pertex Endurance. This offers the benefits of being very light and breathable, while providing sufficient added protection to supplement a tarp. The Endurance isn't technically waterproof, but it is knocking on the door, and I have used mine alone in rain storms without issue. This is what Big Fin had in Nevada this year when his down bag remained dry while unattended in a rainstorm. Rab seems to have discontinued the Ultra Bivy, though it's still on their site, but the
Survival Zone Lite appears to fit the same mold and I'm anxious to check it out when we get some in at
High Caliber Gear.
Ultra Light tents certainly have their place, and I oscillate between them and a bivy, depending on mood, conditions expected, and how my last trip went. The bivy has been getting more use recently because it sets up easier and in more places, can handle most any winds, is lighter and less bulky than all but the most extreme of UL 'tents', and I feel adds a measure of additional warmth to my sleep system. If I can't decide on one for myself, I won't assume I can tell you what you'll be most happy with, though hopefully I'll add an insight of some sort. I am a gear junkie, so I don't think much of having a few different bivys and tents around to use in different conditions, and still try out new gear and my friends setups when I feel something else could be 'better'. Gear today is a plethora of riches.
Regarding down vs synthetic sleeping bags, my short answer without knowing anything about specific conditions is 'it depends'. For the style of trips I do, where I do them, I don't even think about synthetic, and in fact don't currently own one. A few reasons: there is some precipitation where I hunt, but it is generally limited. As far as mountain hunting goes, I hunt pretty dry mountains. Hunts in a lot of Canada and Alaska would require a different perspective on this. It is also rarely humid where I hunt, limiting condensation challenges and speeding bag drying in the event it does get wet. My hunts are often of relatively short duration, 5 nights in the field is about tops for me, and two or three are most common. This gives my bag less time to accumulate moisture, and if it does get soaking wet I have to suffer through it for less time. If I have to bail due to conditions, typically puts less on the line than say a 14 day sheep hunt. Also, contrary to some belief, down bags don't become useless at the first sign of moisture. They just loose efficiency the more saturated they become. One would have to be very soaking wet before you'd be better off without it. The upside of down of course being, I get a lighter, smaller bag that helps contribute to a three night pack of this size (September elk hunts require less cold weather gear and get less optics than deer hunts):
Regarding temperature ratings, they are a pretty personal thing. Complicating matters, bag ratings vary a lot, though in my experience the higher end down stuff is rated pretty accurately/conservatively. The Europeans just came out with a standardized rating system, and they express a bag as a wide range (based roughly on comfy-vs-sleeping-vs-surviving), and also rate a bag nearly 15 degrees different for women. Lots of stuff factors in, and one issue that sometimes bites me is I'll run my tank so dry hunting or hiking, that it will be really hard for me to warm up. That said, I view the bag as just one part of my sleep system, and often count on other items to add warmth. A full bivy or a four season tent like a Hilleberg will often add noticeable warmth vs a standard three season tent. I carry insulated clothing year round, and will put on a puffy jacket in my bag if needed, along with a good beanie and light gloves. One thing that used to get me is I'd be worried about getting cold, zip my bag up all the way with extra clothing on, start to sweat a little, and end up wet and then chilled. I'm very careful now to remove clothing or vent my bag if I feel this coming on. Using some of these techniques I stay pretty comfy to below a bag's rated temp.
Regarding the Montbell's in specific, I think pretty highly of them. I bought my dad a #1 Super Stretch, and recently a #3 UL Spiral for myself. They are good quality down bags with some extra comfort for the Super line (due to the cut and the stretch) and a great DWR that sheds water like a champ.
Thoughts?
