Jun 18, 2012 at 12:56 pm #1291150
@oroambulantLocale: San Francisco
I can't figure out why you would wrap an UL bivy around a UL bag/quilt. What I've seen of UL bivies have momentum or pertex for the top, and that's pretty much what the bag/quilt has. So what functionality is added? Isn't a bivy a replacement for a tent?Jun 18, 2012 at 1:13 pm #1888025
A ul bivy is usually used in conjunction with a tarp to keep rain splatter off your bag and soaking it,it usually has a waterproof bottom to keep the bottom of your bag from getting wet from the wet ground and keeps out drafts since you are not in an enclosed tent.They are not waterproof because that is what the tarp is for and if it can breathe then you are less likely to get condensation.Jun 18, 2012 at 1:31 pm #1888033
@dianodaLocale: Chicago, IL
Basically what Anna said. The functionality added is the extra layer of protection it provides – a momentum fabric top provides bug protection, a limited degree of water resistance, decent wind resistance, and a minimal amount of warmth. Cons – slightly decreased breathability compared to nothing at all, which in certain (although rare) conditions can contribute to excess moisture retention.
An UL bivy works in tandem with a tarp as a replacement for a tent. The stand alone alpine-style bivys can be rather miserable in non-alpine conditions – WPB fabrics aren't anywhere near as breathable as momentum and can become muggy in conditions where an UL bivy + tarp would be comfortable.Jun 18, 2012 at 2:39 pm #1888053
@verberLocale: San Francisco Bay Area
Most UL bivy have waterproof bottoms and DWR tops. If you are using a floorless shelter or tarp the waterproof bottom is a replacement for a groundcloth. Why the top you might ask, especially since the material is pretty much the same as your bag / quilt?
There are three reasons one might find it useful. The first is that it will tend to be more water resistant in the face of water splatter than the sleeping bag / quilt because it has less exposed stitching which tends to let the water into the bag. Second, for quilt users, it can block drafts. Finally, for quilt users, it tends to constrain the quilt… something that I have found useful when using a small groundcloth and tarp, because the quilt would have a tendency to hit the ground beyond the ground cloth.
Yes, bivy waterproof bivies can be used as a tent replacement, but I think the tent replacement bivy are only useful when you have extremely limited space with high winds such as what some climbing trips experience. Otherwise there are options that are lighter than a bivy which provide more space.
–MarkJun 18, 2012 at 3:01 pm #1888058
drowning in spamMember
My bivy provides protection against drafts and bugs, and keeps me a little warmer. It also lets me sleep with my light, watch, maps and guide book pages without concern about those things getting lost during the night. One time it kept mice from directly crawling over my face.
It could provide some protection against rain spray, but I've never expected it to do that.Jun 18, 2012 at 3:53 pm #1888076
With the advent of ul tarp and bug inners, there is really no reason to us a bivy anymore. I have used various kinds and in many of the conditions that I have encountered, I endured copious amounts of condensation. I agree that with the availability of new fabrics for sleeping bags there is significant redundancy with using an additional bivy.Jun 18, 2012 at 4:55 pm #1888098
…Jun 18, 2012 at 5:12 pm #1888102
Poncho Tarp + Bivy still seems lighter than Tarp + Groundsheet + Rain Jacket, at least in many incarnations of that combo.
I've never understood the industry pricing for UL Bivys though, If you consider the low complexity and that exotic materials are not necessary for a light, effective bivy, it doesn't add up.
Here in AZ/NM, at least in 3 season setups, I would be comfortable tarping without a bivy (synthetic bag or at least a dwr outer fabric).Jun 18, 2012 at 5:43 pm #1888114
I've been through all the above combinations, from poncho tarp+bivy to tarp+bivy to solo shelters (Contrail, Fly Creek UL1 and MSR Hubba) and currently think a good sized floorless shelter like a Speedmid, ShangriLa 3, Trailstar, or similar will best all the above. A headnet and some deet can handle the bug issues and with a dedicated carbon pole and polycro groundcloth, all the above combos weigh in at ~2 lbs or less. All of the above will handle all but serious winter conditions, AND you can actually hang out, invite a friend or two in to hang out in a storm, change clothes, cook, and sit up/move around without worrying about condensation or claustrophobia…
Only drawback of the above is the larger footprints…which I've never found to be an issue unless mountaineering.
To each their own, of course.
To me, the tiny tarp (or poncho) + UL bivy would only get carried if I was hellbent on speed/mileage/and the lightest weight possible and comfort was completely secondary. But that's rare.Jun 18, 2012 at 6:05 pm #1888123
@oroambulantLocale: San Francisco
My wife and I have been bringing OR Alpine bivies (2Lbs ea) on a blue tarp. My bag is a 5 Lb 0deg, hers is a Cat's Meow (3Lbs?). I've never pulled the bivy out because we have had outstanding weather.
A few years ago, I hauled a 7 LB 3-man tent and that year we awoke to snow cover and -6 F, everything frozen solid. We weren't expecting bad weather, but it would've been not so good if we weren't huddled in the tent.
Now we are sewing 3.5" loft down quilts and are taking a look at lighter bivies versus UL tent. The ORs at 2+2 Lbs make for a lot of UL tent.
What I REALLY like about the bivies is the near instant setup and tear down.
What I REALLY like about the 3-man tent is it doesn't need staking.
I don't like spending time getting the sleeping setup right.
I have these images of tarps ripped away in the wind because the stakes don't penetrate granite all that well and the Sierra soils are very loose. I am getting better at avoiding katabatic wind tunnels, but I've been surprised at how ferocious it can be just after sunset.
Still mulling the right thing…Jun 18, 2012 at 6:25 pm #1888128
@verberLocale: San Francisco Bay Area
> aren't they getting close in weight to an UL tent + rainfly?
Close if you round to the nearest lb, yup. Close if you consider relative weight.. nope. Tent is a factor of 2x heavier. Of course the tent provides more protected space, but the flip is you have less versatility. For example here are some weights:
a tarp + tie-down cord (guy lines?): 3.5oz
an UL bivy: 5oz
a ground cover (not needed… see bivy)
poles: (n/a since using trekking poles, but if you want to include it, 3.9oz)
Which adds up to 11oz, 14.9oz if you count the pole
–MarkJun 18, 2012 at 6:27 pm #1888130
@ngatelLocale: Southern California
A 8×10 or similar tarp doesn't need a bivy. The lightest set up I have used is a zPacks Hexamid Solo (no inner) and the poncho/ground sheet. This combo covers my rain gear too.
A poncho/tarp requires a bivy in my experience.
A bivy can be a nice compliment to a narrower quilt.
No perfect set-up. Justs takes time, experimentation, and experience to determine what works best for each person.Jun 18, 2012 at 7:06 pm #1888143
@ouzelLocale: Pacific Northwest/Sierra
For ~21 oz and 17 oz, respectively, you can have a Tarptent Sublite Tyvek or a Six Moon Designs Skyscape X, stakes included, both simple solo tents that go up easy, provide ample space, and a bug free experience. Both are good options for the Sierra or other relatively dry environments, not so good for wetter ones.Jun 18, 2012 at 7:08 pm #1888145
Heres a hint … With a synth bag you dont "need" an ul bivy with a decent tarp …. And youll laugh at the condensation gods …
So how much weight are you saving with a bivy+bag vs a synth bag alone … HmmmmmJun 18, 2012 at 7:15 pm #1888148
1) ease of setup especially in drier climates. No full enclosable system weighs less or is as quick to set up.
2) wind protection especially with a quilt. Ideal in SoCal on the windy ridges. You can be completely protected with little to no flappingJun 18, 2012 at 7:16 pm #1888149
Or a warmer, lighter down bag with excellent DWR….Jun 18, 2012 at 8:27 pm #1888173
I have two shelter setups right now: poncho-tarp + MYOG bivy and a Golite SL-3, recently acquired, + …something (groundsheet or bivy, maybe even the matching nest).
Poncho-tarp/bivy: Poncho is 7 oz, bivy is at 6.5, so add in stakes and guylines and I'm looking at probably 18 oz total for rain gear, very good shelter coverage, ground cloth, pack cover, total bug protection, and a nice little bump to my sleep system's rating. I still use a mummy bag, but I plan on making a synthetic quilt sooner or later, so the bivy will help that as well by cutting drafts.
SL-3: Fly is 23 oz if I recall but sheds rain and snow beautifully (so I hear), and it is spacious, even for two people. Better protection from bad weather as well, no matter what is said about a tarp/bivy combo. The downside comes when you consider that I need carry a pole extender, still have to add in stakes, add some sort of ground cover, and the stock nest is ridiculously heavy due to the very tough floor material (because of the center pole trying to stab through it). I also still need rain gear, especially if the weather is bad enough that I'm bringing the SL-3. So carrying the SL-3 adds at LEAST 2 lbs to my pack.
To the bivy point: I wouldn't want to camp in bad weather under a poncho tarp without a bivy, and I wouldn't want a tarp versus UL tents unless it really reduced my pack weight, which a poncho-tarp does. So a bivy gets factored into the weight cost and the tarp/bivy combo still comes out ahead.
-JeffJun 18, 2012 at 8:43 pm #1888180
.? You are comparing the weight of a solo set up with a 3 person pyramid. You could get a Tarptent Notch for less than half a pound increase.Jun 18, 2012 at 9:54 pm #1888199
ahhh … but you cant go HA HA HA HO HO HO at the condensation gods even with a bag with good DWR and more down fill ;)
there is of course the "faff" factor in using a bivy/tarp … IMO less faff is worth a bit of minimal weight, especially when yr cold, tired, hungry and wet … or need to go water the trees in the middle of the night …Jun 19, 2012 at 9:28 am #1888276
David, I realize. Different tools for different jobs. But that's the best answer to the bivy question I can put forward.
-JeffJun 19, 2012 at 9:45 am #1888284
"ahhh … but you cant go HA HA HA HO HO HO at the condensation gods even with a bag with good DWR and more down fill ;)"
Ah come on, synthetic fill gets wet too….! Or does it? Maybe you have a special, one of a kind bag made with unobtanium….Jun 19, 2012 at 9:53 am #1888288
@danepackerLocale: Mojave Desert
Here we go again.
Tarp & groundsheet W/ bivy
v.s. tarp W/ floored bug net
v.s. UL single wall tent.
Having tarped for years I find a UL tent like a SMD Skyscape or a TT Moment is faster to set up and strike and is often lighter than a tarp and floored bug net of the EQUIVALENT MATERIAL. No worry about splash, no double setup.
And you can have the bivy&headnet "solution". I want bugs and creepy-crawlies totally out of my sleeping area.Jun 19, 2012 at 11:23 am #1888303
@hikinggrannyLocale: Gateway to Columbia River Gorge
My ZPacks Hexamid Twin (room for my grandson, my dog and me) weighs 17 oz. including cuben bathtub floor groundsheet, guylines and stakes. Tarp (GG Spinntwinn) plus ground sheet plus bug net (I needed one big enough for both me and my dog) is 6 ounces heavier. Of course there is a bit of a price differential!
I tried a bivy once. It was so slippery that I not only kept sliding off my air pad, but after some tossing and turning the silnylon part of the bivy ended up on top, where it of course caused condensation. It was almost as bad as the silk liner I tried when my sleeping bag was new! About 2 a.m. I tossed the bivy into my pack and never used it again.
My worst experience with wet insulation was with a synthetic sleeping bag. I can tell you from bitter experience that a wet synthetic bag is just as cold as a wet down bag!Jun 19, 2012 at 2:28 pm #1888352
@glacierramblerLocale: NW Montana
If you're sewing up down quilts, then a bivy is a much easier MYOG project. Check out this thread for some more details.Jun 19, 2012 at 4:46 pm #1888397
I don't see the math (weight) nor functionality of a bivy.
First of all, a bivy bottom (used in lieu of a groundcloth), made out of some kind of WPB like silnylon, is almost by definition going to be heavier than window shrink wrap used with a floorless tarp.
By definition, I mean it has to be strong/heavy enough to sew, even @ 1.3oz yrd2. Compare this to really lightweight WP window shrink wrap, which has good puncture resistance, but almost even better, is so cheap ($2-3 for a 7×4) that it can be discarded after a trip.
Secondly, the incremental increase in tarp weight for a full coverage tarp (eg tapered/cat cut 10×8) vs bivy tarp (7×5) is nominal, especially considering you still have to take the same poles, guys, stakes, etc.
Third, coverage is a function of square footage. A 5×7 tarp will cover 35 sf, whereas a tapered/cat cut tarp, starting off @ 10×8 will come in the range of 65-70 sf – nearly 100% greater coverage/protection.
Fourth, if you're using a bag/quilt (either syn/down) built out of a quality DWR, like Teflon coated M50, in combination with a full coverage tarp, then you already have good splash resistance. That is, if any rain was to find its way in.
Fifth, using a quilt/down without an additional layers on top and/or a closed WP bottom (like sil) cuts down on condensation.
Sixth, using high quality insulation (eg 900FP down) will achieve much greater warmth with the addition of 2-4oz vs 4-6 oz of bivy material. If you want extra warmth or want to avoid drafts, simply make the quilt bigger and/or overstuffed. Either option will weigh less than a bivy.
The only advantage I see to using a bivy is the weight saved by using a poncho tarp vs carrying a stand-alone 5×7 bivy tarp. Yet, this 'advantage' also has a drawback – who really wants to hike in a poncho if it's raining? And do you bring along a wind shirt for marginal conditions?
I think many who have experimented with bivy tarp and/or poncho tarp combos have come full circle back to the tent concept, in terms of full coverage, but are simply using over-sized tarps to fill the 'tent' function. That's me.
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