Bivy under tarp — what’s the point?

On the whole I think you're right. If your tarp is so small that you absolutely need a bivy for spray protection, get a bigger tarp and ditch the bivy. The weights will cancel each other out.

My guess is that the bivy+tarp practice is a holdover from a time before DWR fabrics and water-resistant down were standard in bags and quilts. My quilt is made of Argon. What good would it do me to put another layer of Argon on top of it?

The main benefit I've found of bivies is that they block the wind quite well, which can be handy when using a quilt at the edge of its temp range.

The duomid isn't the type of tarp a bivy is needed with. The bivy is usually paired with a 7×9 A frame type tarp. The bivy handles minor rain blown in the end of the tarp, and splatter when you sleep near the side edge. A mid doesn't have either of those problems.

Ps: If you use a larger A frame style tarp you don't need a bivy either :)

Pps: Bivvies do work really well with quilts since they keep it on top of you and block the drafts at the bottom edge. For a sleeping bag, it's not a big benefit.

My experience has pretty much been the same. I've had several ul bivies from several companies. When first making that transition to lighter weight, I bought bivy/tarp/quilt combo because that's what I was learning from others. But for me, the quilt was always drafty without the bivy and the bivy created quite a bit condensation. I used both large cat cut tarps and 8×10 flat tarps, and while I loved the openness, I didn't enjoy using them in heavy rain and wind. Using a mid, I didn't need a bivy, but then my quilt was still drafty.

So I ditched the bivy (for the second time), went back to sleeping bags (a zpacks for ul trips, and WM for overnighters), and with the MLD Patrol Shelter Duo, found that balance of using a tarp with the protection of a mid.

For your situation, I would agree with your assessment that it seems like you are better off without the bivy. Thing is you have a MLD Duomid that offers a lot of protection, and so long as you are fine with sleeping with a bug net on your face, then you're good to go with the Mid and a polyco ground cover.

I too did an experiment with my bivy, as I wanted to test it at home before I took it out in the field. I own a Borah Cuben bivy, and after the experiment I was bummed out by the condensation as well–and I probably got more than you, as mine has an M50 top rather than Argon. Then it occurred to me that I could modify my bivy to address the issue of condensation, because a bivy really works for me for a lot of my section hikes. After I put in a condensation vent in my bivy, it has worked great. Only very minor moisture in the foot box, and that's only some of the time. You can read more about this mod here if you want:

http://cesarandthewoods.blogspot.se/2013/05/section-hike-and-bivy-modification.html

But I understand my bivy's limitations. For me it shines great when I take it with a flat tarp, and especially on trails that have a lot of trail shelters like the ones I generally hike here in Sweden. I get bug/slug/mice protection, wind blockage, rain spray cover–not to mention it's easy to set up, great for cowboy camping, and also to use inside of trail shelters (and tarp can be used to pitch a front door for the shelter if wanted/needed). And my bivy only weighs 145g with stuff sack, which is less than half of what say most net tents weigh.

However because I have been doing more involved/isolated section hikes as of late, this got me to re-evaluate my shelter choices. And I recently bought a net tent to try out with my flat tarps. As much as I love my bivy, I want to see if I like a net tent more. One big pro of the net tent over the bivy is space to chill out in, which or me I have craved more as I am going on more challenging and far-off trips. I also would like to do thru-hikes in the future, and on paper I think I would probably go with a flat tarp and a net tent rather than my bivy, but still gotta try my net tent out (the order is still being processed).

Anyhow, hope this helps. Go with head net and ground cover with your Mid, and maybe consider an inner net for the mid in high critter season.

yeah. I'm going through the same realization. I

planning to eventually switch to a net-topped bivy once I settle on a pad (rectangular v tapered) or skip it altogether.

When I started backpacking I bought a Mountain Hardwear Micro Mesh bivy. It weighed over a pound and had what seemed like 14 miles of zipper to mess with. I used it twice under an 8 x 10 flat tarp and after a prolonged hard rain on trip number two I realized it was a complete waste of pack space. With my tarp pitched fairly low even that powerful rain couldnt reach me. The shell of my MYOG quilt resisted wind well enough that I was warm all night. Bugs are not usually a big problem for me, a head net and DEET suffice.

Here's the math as it adds up for me.

182g (bivy) + 207g (5×7 poncho) + 53g (stakes+lines) = 442g

The poncho is small enough that I need some spray protection with the bivy. It's M50 black and hasn't condensed yet. From reading, I've just been fortunate and simply haven't used it enough.

However, if I were to get a cuben 7×9 tarp (150g) I could save some weight if I had a rain jacket that was less than 240g. If the tarp were a poncho I could do away with the jacket too.

… now that is something to consider.

Depends on conditions. Used with a tarp-

A bivy in windy Joshua Tree, eastern Oregon or the Canyonlands in cooler months is warmer than a roomier tarp alone. No condensation when there is a dry wind.

Hot buggy weather a bivy is much nicer than just a headnet with a hot sleeping bag or quilt. No fun trying to get buy with just a tarp and headnet on summer treks north of the arctic circle or canoeing in Wisconsin.

Snow caves or drifting snow, put your pad inside and keep snow from falling on it and melting in to your sleeping bag/quilt as
well as keep track of your boots etc. without having them inside your bag.

Windy, dusty conditions can be more pleasant with a bivy.

When packing for a living, a bivy can help keep your spendy down bag cleaner, (and a liner too) and hey, you're in shape and don't notice the extra weight then anyway. I used to bring hardback books to read and reference when teaching.

With a full bag in that shelter a bivy is doing more harm than good. I does great as a wind block when used with a quilt. Or for splash protection when used with open tarp.

Now for the tough question. Are you sure that you were wetter without the bivy. I suspect under identical conditions that you would have condensation within your bag, not on your bag as you saw when using your bivy. You likely moved the dew point out between the bag and bivy at least partially.

The difference between the two nights is most likely due to different ambient conditions. Some can be very local or subtle but mean a very different end result as far as condensation goes: a slight breeze, a few degrees more or less, a slight delta in relative humidity, the orientation of your tarp, tree cover, altitude, natural windbreaks, valley bottom, slope, crest, flats locations…

The bivy will help keep your bag's shell away from the dew point, which is good, but at the same time it's more prone to get condensation itself, being further from your body heat but this is really splitting hairs compared to the bigger factors above.

Yeah, generally, for the extra weight of carrying a bivy, you are better off with a larger tarp.

When camping, water problems with a properly sized tarp are usually avoided(I like a larger, 1lb shaped tarp w/beaks.) This is large enough to avoid water, small enough to avoid set up problems, and, is voluminous enough to cook under in bad weather. It is *just* large enough to have a small fire for warmth near one edge, if needed.

Water under the tarp is more of a site selection, set up issue, but I have to do this with whatever tent/tarp I carry and is not really considered.

I see this as a two part problem: Condensation, bugs

Condensation is a problem with bivies. As others have said, I wake up wetter inside one, than not using one. Unless I devote a large amount of time drying out my bag/quilt, this problem can be worsened over a couple nights, leaving me colder at night than if I didn't use one. I don't care for the fiddle factor of playing with two coverings every night either. It is just one more layer I have to deal with. In very heavy wind storms (40mph with gusts to 60mph) sometimes I get a little spray. Then I have to dry things out, but this is not the usual.

I live/hike in the north-east USA, so bugs, especially black flies, mosquitoes, and deerflies are a real problem. A simple 2-3oz net thrown over my head and arms is all I need, and, only in high summer. I get a few bites. It seems that I get one or two while sleeping on a week trip out. Not badly bitten, and, nothing I cannot deal with. I don't bother to bring the net in fall or spring, because the nights are well below the temps that the bugs become inactive. Often in summer, too, but I cannot count in it. I guess they just got 3" of snow in the ADK's a couple days ago and the ponds and lakes are still frozen…

There are a number of very good articles on this very subject but you have to be a member to read them( I will link them in case someone else would like to read them or you decide to get a membership)
Staying Dry in a Bivy Sack: Techniques for Managing the Moisture Balance Between External Precipitation and Internal Condensation

Bivy Sack Technologies, Products, and Applications

Condensation in Single-walled Shelters: Contributing Factors and Tips for Reduction

Night Time Condensation on Tarp and Tent Fabrics

This one you can read, it is written by BPL member Alex The Bivy Condensation Condundrum

If you do a Forum Search you will find numerous threads on this subject

In the Mid-Atlantic, I have pretty much found that a bivy is completely redundant if I am under a tarp or in any kind shelter. And as "breathable" as Argon might claim itself to be, if it is less breathable than your sleeping bag, then it is probably going to hinder moisture control more than help it (as your experiment has proven.)

This, in my opinion, is where "protection" vs. "comfort" clash, especially in our rather humid climate.

However, I cherish my 50d EE Enigma quilt, and would generally prefer it not get sprayed or dirtied by stuff. Therefore, I've recently been using a silk liner as a pseudo-bivy, to essentially mitigate any of the unlikely spray, dirt, or spills which might happen. It also can adds a slight uptick in the comfort range of my system, and I don't feel obligated to attach the straps to the underside of my pad(S). In fact, I typically pull my 1/8" foam pad into the silk liner with my quilt, and leave my NeoRest on the outside of the system.

So the liner takes the beating, and I have no trouble dropping my silk liner in the next stream I walk by, just to give it a quick rinse if I need to. And if it doesn't dry out in enough time to sleep in it, it's not the end of the world.

If you have one around, or something like it. I highly recommend trying it out in this way if you ever feel the need to "protect" your sleeping bag, but not yourself.

Matt

I might have a interesting experiment/case study for you.

Last winter I tried the following setup but with the bivy only halfway on my bag.
BA 0 degree bag
SOL emergency bivy, with about 24 1/2" "breathing holes" cut into it.
ccf 1/8" pad
Go-Lite poncho/tarp
no groundsheet

Outside conditions:
5-11 degrees F
15-18 inches snow
Wind 0-5 mph
continuous snowfall, large flakes
Tree covered ridgeline

I pulled the bivy upto my waist with the idea that if I got cold I could pull the bivy up farther, or kick it off if I got too hot.

Results:
Didn't wake up once, so I only have morning observations.
Snow melted down about an inch from where I stomp,packed it. No water seems to permeate the CCF pad, bottom of bag was dry.

Sleeping bag had noticeably more crusty ice (frozen condensation from perspiration) near my legs which were inside the bivy. My upper body (outside the bivy, was almost frost free. Still had a bit. "Noticeably more crusty" means the ice crystals were larger inside the Bivy(upto 1 inch spots) and more frequent (5 times more dense). Outside the bivy, ice crystals were more "pencil eraser sized" and less dense. UnBivied section of the bag barely had to be shaken out at all. Bivied section had to be hit with my hand several times to beat the ice off before stuffing the bag.

Other experiments:
Overquilt in Copper spur tent no rainfly. 20F Overquilt built up some ice, but sleeping bag stayed ice free. Did not feel wet.

Sleeping bag only in tent with rainfly. 0 degrees, ridgeline, wind ~10-15mph No Ice on bag. Outer tent had ice crystals.

Conclusions, Unless I'm sleeping alpine, between two boulders and preferably in west coast, low humidity conditions, I don't plan on using bivies due to condensation/weight issues. Mid atlantic is just to humid imo.

> Sleeping bag had noticeably more crusty ice (frozen condensation from perspiration) near my legs which were inside the bivy. My upper body (outside the bivy, was almost frost free

not a fair comparison. Torso generates more heat than legs while sleeping. Your result is to be expected regardless of bivy use.

The issue with your experiment, is if you had swapped what you did different nights, you may have had the opposite results. As a general rule, I sleep drier with the bivy then without no mater what conditions I'm in.

The point of the bivy is that it is used even when cowboy camping when the tarp isn't needed. Whats the point of setting the tarp up when it isn't going to rain is the question. As someone who cowboy camps more often than not, a bivy fits my camping style. I've been using a bivy since 2007 and a tarp since 2006 in most conditions except true winter (shoulder season snow is about all I see), and I really like using my bivy. Used it on the PCT and the northern part of the AT. Tried a Zpacks Hexamid last summmer but came back to the tarp/bivy. That said, what works best for someone in one location may not work best in another with someone else.

– Bivy provides wind protection (important in the high country where you are exposed to high winds).
– It provides bug protection. Using a headnet works and I often have done that. But it requires you to bundle up tightly in your sleeping bag quilt. When its warmer, I sometimes just sleep in the bivy without my quilt.
– Can act as a ground cloth. Sometimes, I use my bivy but leave it unzipped and flipped open.
– Can add warmth during colder weather or allow you to use a lighterweight quilt/sleeping bag.
– Extra rain protection. Yes it provides some splash protection under a small tarp though in strong wind, even that larger tarp may seem small with the way the wind is gusting the rain under. I hate camp chores like setting up a shelter, so I really push my luck with weather. Most of the time I get away with it, but not always. I've been awaken by light rain during the middle of the night where the bivy does provide some rain protection before saturating. For light rain, drizzle, or just a passing shower, just being under a large tree in the bivy works enough to stay dry inside. And when it the rain doesn't look like its going to stop anytime soon, it gives you some time to setup the tarp before you down quilt gets wet.
– With a quilt, it can remove drafts from those that move alot during the night. Or keep someone from having to buy that heavier extra wide quilt to compensate for their poor sleeping habits. Personally, I use a narrow quilt and have no issues with drafts, even without the quilt because I've trained myself to tuck when I flip over even when half asleep. But not everyone is able to do that.

If you only think of a bivy as extra rain protection, then maybe its not necessary with some of the shaped tarps such as a mid. My borah gear cuben fiber bivy only weighs 4.5oz, but there are some shaped tarp options that would bring the weight to be under my small tarp+bivy combined weight (12.5oz) if you don't need the bivy.

As for condensation, the more breathable fabrics of some bivies makes that less of an issue, as does campsite selection with dew. This isn't to say that it isn't a problem, but I rarely have an issue out west where its drier and didn't notice a big issue with it on the northern half of the AT in late summer/fall (still haven't tried the southern half though so maybe my opinion would be different after I do. Though being able to use it inside the AT shelters was nice).

I think part of it depends on where you go. I typically backpack in drier climates, such as the Sierras. For me, the tarp is protection from rain or wind when needed. On nice nights, the tarp stays in the backpack. It's also nice to be able to setup "camp" real quickly without worrying about getting the tarp positioned right. I often arrive to camp a couple hours after sunset, so it's great when the weather is fair and I can just plop down my bivy and sleeping bag.

I also like the protection from the bugs, whether it's mosquitos, spiders, scorpions, beetles, or whatever else. I could wear a bug net, but then a bug could just crawl into the bag anyway. I don't have any phobias or anything, but still, I'd rather keep myself separated from them.