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?

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.

Edited by annapurna on 06/18/2012 14:14:23 MDT.

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.

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.

--Mark

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.

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.

so for the person who will opt for this setup:
a tarp + poles + tie-down cord,
a bivy,
a ground cover + stakes (or some use trail rocks)

cost aside, aren't they getting close in weight to an UL tent + rainfly?

example:
Big Agnes Fly Creek UL1 Tent Specs
advertised Packaged weight: 2 lbs. 3 oz.

or
MSR Carbon Reflex 1 Tent Specs
2 lbs. 9 oz.


since the minimalist way is a couple of cliff bars away in weight, from the high end UL solo tents, cost aside, the UL tent option is not that heavier in contrast.

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).

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.

Edited by xnomanx on 06/18/2012 18:45:29 MDT.

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...

> 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)
stakes: 2.5oz

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

--Mark

A 8x10 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.

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.

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 ... Hmmmmm

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 flapping

Edited by gg-man on 06/19/2012 05:19:43 MDT.

Or a warmer, lighter down bag with excellent DWR....

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.

-Jeff

.? 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.

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 ...

David, I realize. Different tools for different jobs. But that's the best answer to the bivy question I can put forward.

-Jeff