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Topic: Bipitty, bobbity, Bivy, Condensation sucks< Next Oldest | Next Newest >
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PostIcon Posted on: Oct. 24 2012, 11:26 pm  Skip to the next post in this topic. Ignore posts   QUOTE

So i've been doing a lot of reading, research, and thinking about Bivy's lately.  Read a lot of informative posts over at the back packing light forum, and read reviews of different bivy's at different places.

 Seems the most common complaint (which is pretty common) about them is condensation, even in many of the so called breathable, waterproof kinds (i've heard mixed things about eVent bags).   I already have a poncho tarp, and figure it would be cheaper going with a bivy than an UL tent even though there are certain aspects of the latter that do appeal to me.  

    Besides liking to hike, camp, etc, i'm also preparing for the SHTF stuff that i feel is coming within the next couple of years or so, so I'm trying to strike a precarious balance between lightness, durability, comfort beyond the weight issue, and affordability.  

 Definitely is proving to be a challenge to fit all criteria well.  Here's one idea for a home made bivy that i've had, and i'm kind of inspired a bit by the popularity of Polartec's NeoShell fabric, which in some ways seems to be just an amped up, slightly revised version of their previous Powershield stuff.  

 NeoShell seems to be the first truly breathable and yet sufficiently waterproof fabric out there.  Yet, i've heard plenty of good things about Powershield as well.  Sooo, i decided to do the "unthinkable" and shirk convention yet again.  

 I went over to Questoutfitters and checked out their fabric (and looked at other sites and company's like Discovery Trekking, Zpacks, Thru-Hiker primarily).   I saw this stuff under "fleece fabrics": SOFT SHELL -  LIMITED QUANTITIES
WT/SQ YD=apprx  4.5 oz.    This fabric features a tri-layer construction with a windproof / water resistant / breathable urethane laminant sandwiched in between an outer shell fabric that is treated with a durable water repellant (DWR) finish and a lightweight fleece on the backside.  This construction combines both a premium outer shell fabric and a fleece together with a little stretch for the ultimate IN   comfort.  A lighter weight and more packable alternative to using an outer shell and separate fleece lining.    Uses: jackets, hats, mittens, skiwear etc.  Wash Code =2, 3
1-15 YDS 15 YDS-ROLL SZ ROLL SZ
#1604             56" $20.95 yd"

  It sounded a lot like Polartec's Powershield stuff...  Quest outfitters didn't say exactly what the stuff was, but they confirmed it was Polartec made or associated.  It was similar price to some of the Powershield stuff over at Discovery Trekking.

  I ordered two yards of that.  I know it's somewhat heavy compared to many of the WPB fabrics out there, but i think it will really cut down on the condensation issue if it is or is akin to the Powershield fabric and will provide just enough water resistance for use under a smaller tarp.  Also, for having a little fleece added it is not that heavy (my quilt would probably rate around 40, so i would welcome the extra warmth).  In any case, I won't be using the full two yards, some is definitely coming off around the feet.

   Also, it seems like it will be a lot more durable than a lot of the super light WPB fabrics I've seen, with the exception of the uber expensive ones like the Cuben Fiber one, etc.  Big factor for me--it needs to last and in constant use conditions.  

 The great thing about NeoShell and Powershield is that they allow "just enough" outside air and wind to blow through the fabric to  help with convention of water vapor.   If i had the moola, I would go with the Neoshell fabric being more truly waterproof, but it's 40 dollars a yard at Discovery Trekking--that's twice what I'm paying for the above fabric.  And that's supposedly a "sale" : 0

 This fabric will be just for the top.  For the bottom, again at Quest outfitters, i saw this fabric under "coated":  HEAVY COATED OXFORD
WT/SQ YD=approx 5.0 oz.   100% nylon fabric with 1 1/2 ounces of  polyurethane coating (approximately 3 times the usual amount of coating).  Uses: great for bivy and tent floors  when the ultimate in water protection is needed.  Wash Code= 1     ROLL SIZE = 100  YDS
1-15 YDS 15 YDS-ROLL SZ ROLL SZ
#1047             58-60" $7.95 yd $7.49 yd $6.25 yd

 Again, a bit heavy, but it sounds like it will be very durable and VERY water proof, but yet not so expensive like some of the other fabrics i would prefer because of their lighter weight (again, Cuber fiber comes to mind).  So i ordered two yards of that, but again won't use all 10 oz's of it.  

 Here's where i'm a bit conflicted, and i will continue this on another post since this one's getting long.  TBC...
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PostIcon Posted on: Oct. 24 2012, 11:42 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

So, the conflict--do i sew the Oxford material and Powershield like material together in a true bivy style way, OR do i cut down on condensation some and increase flexibility of setup & storage some by rolling up and just sewing the sides a bit up on the Oxford material and use it more as a ground tarp but more tub style?    Then use the Powershield like fabric more like a quilt, sew in a foot box area and just wrap it around me?

 Certainly the former would be better protection against the bugs and  outside wetness (it probably would increase internal condensation some).   However, whether i sew the two together or not, i will be adding plenty of No-See-Um mesh to the WPB "fleece" material.

 One of the things i don't like about some (many?) Bivy's is that they have too much of the mesh inside the actual bivy, so that if it's really hot and humid out, if you want protection from the bugs, you still have to crawl inside to some extent.  So i plan on sewing the mesh fully on the outside (with a little extra slack so it can be lifted up) with maybe a partial zipper side system, so if i want to, i can sleep just on top of the bivy and bag/quilt with only the raised mesh covering me.  

 Anyways, if anyone here is interested, i can eventually put up some pics of the h.m. bivy system.  If anyone has any good ideas or suggestions about whether to sew or not to sew the bottom and top material together, i definitely welcome feedback too.
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PostIcon Posted on: Oct. 25 2012, 7:06 am Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Sounds like a fun project. I have no idea how I would sew it. But, I look forward  to your results. Please post photos when done.

But for me with so many 2 pound or sub 2 pound solo tents out there I just can't think how I could ever go the bivy route.


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PostIcon Posted on: Oct. 25 2012, 10:29 am Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

A few thoughts: I've owned a bivy for many years. I use it primarily as a supplement to my floorless shelter and as an "emergency" backup shelter for winter. If weather is good, the bivy works fine by itself. However, it sucks to be stuck in a rainstorm or in big snow dump. I have the OR Advanced bivy which is a bit roomier than most. I have not had issues with condensation once I learned to use it properly. You don't just climb inside and zip it shut. It needs to be ventilated just like your tent. If you overheat inside...condensation will form. If you regulate your temps and only put it in storm mode when it's stormy, it will work fine. It's a basically a hybrid tent. Here is a picture of the model I use.



I would get a tarp shelter for the same weight if I was looking at my primary shelter. Having no place to hang out in a rainstorm just isn't worth it. I also wouldn't consider making a bivy unless I was prepared to make it "bombproof".


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PostIcon Posted on: Oct. 25 2012, 2:30 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE


(eggs @ Oct. 25 2012, 7:06 am)
QUOTE
But for me with so many 2 pound or sub 2 pound solo tents out there I just can't think how I could ever go the bivy route.

I completely understand the above.  The main thing which is keeping me from getting a more U.L. tent type set up is cost and durability.  

 I have a lightish tent already which has a stove jack, which is for my wife, a possible future kid, and i for the possible SHTF scenario, but i figure there may be times wherein we may have to separate and so i want a portable, relatively light, and very durable system if need be.  

 And at this point, i'm trying to do so cheaply and have a very durable system that can take a lot of abuse.  I'm not sure how durable in the long run some of those UL tents are, especially if they were being used a lot and under rough conditions.

 I will put up pics when it's done.
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PostIcon Posted on: Oct. 25 2012, 3:06 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Tigger wrote,  
QUOTE
A few thoughts: I've owned a bivy for many years. I use it primarily as a supplement to my floorless shelter and as an "emergency" backup shelter for winter. If weather is good, the bivy works fine by itself. However, it sucks to be stuck in a rainstorm or in big snow dump.


 I have a poncho tarp i plan to use with it during rain/snow conditions.  


QUOTE
I have the OR Advanced bivy which is a bit roomier than most. I have not had issues with condensation once I learned to use it properly. You don't just climb inside and zip it shut. It needs to be ventilated just like your tent. If you overheat inside...condensation will form. If you regulate your temps and only put it in storm mode when it's stormy, it will work fine. It's a basically a hybrid tent. Here is a picture of the model I use.


 Good points about ventilating and adjusting it.  That is one of the reasons why i'm tempted to not even sew the water resistant, breathable fabric to the waterproof floor.  I could use it more like a quilt and adjust as needed and it would allow me to get in and out very quick if need be.  Might glue some loops or what not on it so i can lift it up a bit and tie to the tarp if need be.  

 One of the common problems of condensation in a bivy seems to be the tight sewing up of a waterproof under fabric to the water resistant fabric.  I really think if there is a separation there, it will gather less condensation... but i don't know that for sure.  

 However, if the material i ordered is polartec powershield or close to it, it will be very breathable--more so than even eVent material.  This is itself will help to cut down on some of that.  It will allow little wind to go through, not enough to really feel (especially if i'm already in a bag).


QUOTE
I would get a tarp shelter for the same weight if I was looking at my primary shelter. Having no place to hang out in a rainstorm just isn't worth it. I also wouldn't consider making a bivy unless I was prepared to make it "bombproof".


 I've considered just getting or making a larger tarp instead of using my poncho tarp, and making or getting a bug net hanging tent with a WP bottom rather than doing the Bivy thing.  But I like to use what i have and i got the poncho tarp for pretty cheap when a local outdoors store closed.  

  Since this is ultimately more long term survival oriented than just light hiking, i may pony up the money and invest in some better quality and more durable stuff.  

 Some Cuben Fiber components would be nice, at least for the ground cloth and tarp.  They now make a WPB cuben fiber material, but i question how actually "breathable"  it is.  

 My ideal set up bivy wise at least, if i had the money, would be a "heavier" Cuben Fiber tarp some 7x9 feet, a "heavier" Cuben Fiber ground cloth in tub style (edges rolled up and sewn on the top of the corners), some 'nano' no-seem-um netting, and some thinner Polartec NeoShell fabric on top (with a sewn foot box).    But that would be pretty darn pricey!  

 Maybe this might give some of you wealthier folks out there some good ideas though.  But like Eggs said, in most cases why not just go with UL tent..   That's what i would do if i had the money and was only looking to hike light.
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PostIcon Posted on: Oct. 25 2012, 5:30 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

check this video on youtube for a lite airy tent.
video link
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PostIcon Posted on: Oct. 25 2012, 9:47 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

If your needs are "survive the Zobie Uprising" you want the most durable, long-lasting, bullet-proof materials available. The military does not buy UL gear.

I know you think I am picking on you but look at the pic I just posted today that was taken yesterday. The rain shell jacket is a Marmot Super Mica, the pants are GoLite Tumalos. But when you see me on a mountain in winter they will be 3-layer shells that weigh twice as much. Why? Because then I want bomber not lightweight.

Gotta leave to help a friend...

Sorry, I'm back.

If you want durable don't worry as much about weight.

As far as your two-piece bivy, what is that? A ground cloth with a tarp over it? A bivy is a pretty narrow category item. If I need to survive I want a better shelter. If I need one in my pack for a possible night on the mountain, or to keep my bag dry under a tarp in the rain, then yeah, a bear burrito might be OK.


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PostIcon Posted on: Oct. 26 2012, 12:40 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Hi Ray,

 I agree with you more or less.  Since I will be carrying more stuff than i would on just a normal hiking trip where i know i will be coming back to the creature comforts of civilization so called, i'm trying to strike that balance between durability and weight.

 I have a decent tent already, which is for my wife and i--i just want a bivy for any possible solo scouting type trips or the like.  I have a "bombproof" backpack.  It's a Vaude cordura model that weighs slightly under 4lbs.

  RE: durability, what do you think about the materials i ordered for the bivy?   Do they seem more durable to you?   They are definitely a lot heavier than the UL fabrics that i've seen.  

 The ground cloth or bottom of bivy is "Heavy Coated Oxford" which is 3.5 ounce per square yard 100% nylon with 1.5 ounce of PU coating.   While I'm not sure, I think the top material is a lighter weight version of Polartec's Powershield, and it comes in at 4.5 ounces WT/SQ YD.

  So far, i think the weak link in this system is my Sea To Summit UltraSil Poncho Tarp.  I probably need a more heavy duty tarp if i want it to last...  What material would you recommend for that?

 (as an aside, i just recently read that Cuben Fiber even has some disadvantages to, and that Silnylon is in some ways better when it comes to tearing at a structural level).  

 Re: the heavy issue, i doubt the majority would be interested, but a couple may be, to get around the heavy issue if the SHTF, i got once of those bicycle children tow along things which converts into a push "stroller" as well.  It's rated for 2 small children at 100lbs total.  It's pretty light weight (i think about 27 or 26 lbs), has two decent quality, smaller bicycle wheels on it, and i figure with a little reinforcing i can put most of my heavy stuff in there like food, my relatively light but very durable Fiskars wood splitting axe, my compact shovel,  my compound bow, titanium wood stove, etc   The bare essentials along with a little food will go in my wife's and my backpack.  

 P.S., gotta watch out for those Zobies, pretty scary creatures they be.
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PostIcon Posted on: Oct. 26 2012, 12:57 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE


(oldnolder @ Oct. 25 2012, 5:30 pm)
QUOTE
check this video on youtube for a lite airy tent.
video link

Wow, he did a great job with that!  I don't think my sewing skills are up to par to make something like that well right now myself, but i do think the concept is pretty good.  I'm curious how it would handle in really high winds though.  Once you have a specific "shape" like that, it lessens the flexibility to set up the tarp in different ways and adjust accordingly to more extreme conditions.  

 But awesome design and application for your average hiking trip, etc, but probably not the most efficient system for what i'm looking at and may need it for.
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PostIcon Posted on: Oct. 26 2012, 1:04 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE


(LiteMan @ Oct. 26 2012, 9:57 am)
QUOTE

(oldnolder @ Oct. 25 2012, 5:30 pm)
QUOTE
check this video on youtube for a lite airy tent.
video link

Wow, he did a great job with that!  I don't think my sewing skills are up to par to make something like that well right now myself, but i do think the concept is pretty good.  I'm curious how it would handle in really high winds though.  Once you have a specific "shape" like that, it lessens the flexibility to set up the tarp in different ways and adjust accordingly to more extreme conditions.  

 But awesome design and application for your average hiking trip, etc, but probably not the most efficient system for what i'm looking at and may need it for.

Something that low to the ground will have little issue with wind. You could easily add center guy outs if desired. The door entrance with exposure to rain is the only major weakness I see in the design (besides the drip line which someone already suggested in his reply area).

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PostIcon Posted on: Nov. 09 2012, 12:57 am Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

quick update.  I finally finished the bivy.  Came out pretty decently, though i wish i had a little more extra slack in the bug netting.  I'm going to probably take some pics of it and put them up this weekend.  I'm also working on another project called Quilt, part deux of which i'm almost finished, but waiting on another order of Climashield Apex material.  I'll probably start a thread about this and the idea.
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PostIcon Posted on: Nov. 11 2012, 7:14 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

pic of bivy with zipper closed and netting set up:

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PostIcon Posted on: Nov. 11 2012, 7:19 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Pic of bivy with netting unzipped and partially rolled up:

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PostIcon Posted on: Nov. 11 2012, 7:24 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Pic of bivy used in a "quilt" application:  (there is a semi/partial foot box area)

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PostIcon Posted on: Nov. 11 2012, 8:09 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE


(LiteMan @ Oct. 25 2012, 3:06 pm)
QUOTE
Tigger wrote,  
QUOTE
A few thoughts: I've owned a bivy for many years. I use it primarily as a supplement to my floorless shelter and as an "emergency" backup shelter for winter. If weather is good, the bivy works fine by itself. However, it sucks to be stuck in a rainstorm or in big snow dump.


 I have a poncho tarp i plan to use with it during rain/snow conditions.  

I think the point was that it sucks having no room to move around.  A poncho tarp probably won't alleviate that unless you plan to run line and hang it 4 feet above the bivy, but even then . . . I think tigger is using his inside a fairly large tarp.

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PostIcon Posted on: Nov. 11 2012, 9:41 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

I don't know, but i see what you're saying.  I've thought of getting a bigger tarp.  I've been adding onto my poncho tarp, but if i add more i have to devise a way to fold some of it up to still be able to use it as a poncho.  Might put some velcro on the inside to pull it up.
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PostIcon Posted on: Nov. 11 2012, 10:43 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Riding out a storm in nothing but a bivy is no fun, even if only for a few hours.

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PostIcon Posted on: Nov. 12 2012, 12:30 am Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE


(no_granola @ Nov. 11 2012, 10:43 pm)
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Riding out a storm in nothing but a bivy is no fun, even if only for a few hours.

+1.

Bivvies were intended originally for climbers on high altitude ridges where condensation meant ice crystals which are easily dealt with.  Not rain.


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PostIcon Posted on: Nov. 12 2012, 9:35 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE


(FamilyGuy @ Nov. 12 2012, 12:30 am)
QUOTE

(no_granola @ Nov. 11 2012, 10:43 pm)
QUOTE
Riding out a storm in nothing but a bivy is no fun, even if only for a few hours.

+1.

Bivvies were intended originally for climbers on high altitude ridges where condensation meant ice crystals which are easily dealt with.  Not rain.

If we're going to speak traditionally, then it's important to point out that these mountaineers traditionally were generally not using tarps in combo with a bivy.  

 There are a good amount of people that just go with a medium to largish size tarp, ground cloth, and their bags/quilts, and sometimes a bug net when conditions call for it.  I know this from having read many posts at BPL.

 I fail to see how camping with a WPB Bivy/G.C. AND a tarp is somehow going to be worse than the above somewhat common system, when it is offering extra rain protection?

 In my particular case, i can see and agree that maybe my poncho tarp may not be big enough to offer enough main weather protection in and of itself.   However, i added a foot to the length and may add another foot or two to the width.
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PostIcon Posted on: Nov. 12 2012, 11:25 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE


(LiteMan @ Nov. 12 2012, 9:35 pm)
QUOTE

(FamilyGuy @ Nov. 12 2012, 12:30 am)
QUOTE

(no_granola @ Nov. 11 2012, 10:43 pm)
QUOTE
Riding out a storm in nothing but a bivy is no fun, even if only for a few hours.

+1.

Bivvies were intended originally for climbers on high altitude ridges where condensation meant ice crystals which are easily dealt with.  Not rain.

If we're going to speak traditionally, then it's important to point out that these mountaineers traditionally were generally not using tarps in combo with a bivy.  

 There are a good amount of people that just go with a medium to largish size tarp, ground cloth, and their bags/quilts, and sometimes a bug net when conditions call for it.  I know this from having read many posts at BPL.

 I fail to see how camping with a WPB Bivy/G.C. AND a tarp is somehow going to be worse than the above somewhat common system, when it is offering extra rain protection?

 In my particular case, i can see and agree that maybe my poncho tarp may not be big enough to offer enough main weather protection in and of itself.   However, i added a foot to the length and may add another foot or two to the width.

Correct, but those mountaineers didn't encounter rain.  They encountered high winds and snow which is far easier to deal with.

WP bivvies don't breath sufficiently if the dew point is at the bivy fabric.  You will end up wet.  This can, and often does occur even if using a tarp.


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PostIcon Posted on: Nov. 13 2012, 1:44 am Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE


(FamilyGuy @ Nov. 12 2012, 11:25 pm)
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(LiteMan @ Nov. 12 2012, 9:35 pm)
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(FamilyGuy @ Nov. 12 2012, 12:30 am)
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(no_granola @ Nov. 11 2012, 10:43 pm)
QUOTE
Riding out a storm in nothing but a bivy is no fun, even if only for a few hours.

+1.

Bivvies were intended originally for climbers on high altitude ridges where condensation meant ice crystals which are easily dealt with.  Not rain.

If we're going to speak traditionally, then it's important to point out that these mountaineers traditionally were generally not using tarps in combo with a bivy.  

 There are a good amount of people that just go with a medium to largish size tarp, ground cloth, and their bags/quilts, and sometimes a bug net when conditions call for it.  I know this from having read many posts at BPL.

 I fail to see how camping with a WPB Bivy/G.C. AND a tarp is somehow going to be worse than the above somewhat common system, when it is offering extra rain protection?

 In my particular case, i can see and agree that maybe my poncho tarp may not be big enough to offer enough main weather protection in and of itself.   However, i added a foot to the length and may add another foot or two to the width.

Correct, but those mountaineers didn't encounter rain.  They encountered high winds and snow which is far easier to deal with.

WP bivvies don't breath sufficiently if the dew point is at the bivy fabric.  You will end up wet.  This can, and often does occur even if using a tarp.

At which point the whole reason for going with a bivy & tarp is moot and you might as well just get in a tent . . . unless it's winter.  

Then again, different strokes for different folks.  If you try it and it works for you then roll on.


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PostIcon Posted on: Nov. 13 2012, 12:09 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Familyguy wrote,
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WP bivvies don't breath sufficiently if the dew point is at the bivy fabric.  You will end up wet.  This can, and often does occur even if using a tarp.


 I thought long and hard about this and general condensation issues after having read many posts at BPL about bivy's (there, most either loved or hated them it seemed, but most did agree on condensation).  

 This is why i chose the fabric i chose despite the weight increase.  As far as i know and can tell it either is or is akin to Polartec's "Powershield" material, which is highly breathable as far as WPB type materials go--much more breathable than even eVent. (technically Powershield is considered more highly, highly water resistant than true "waterproof")

  The other way i addressed this issue was by not sewing/attaching the waterproof ground cloth material to the WPB material, this allows both more general air flow and flexibility to use the bivy in a more quilt like way.

 As far as i know, no one has tried this combination of using an alternative fabric to the typical kinds of WPB's ones usually used for Bivy's (because of their lower weight) and having a gap between the WP ground fabric and the WPB stuff.


 Re: No Granolas comments about just getting a tent--again i understand that sentiment but 1. i don't have the money to throw at a UL or even decently light tent and 2. i'm looking for long term durability.  

 I thought about making a tent myself, which would be cheaper, but i just don't have the necessary sewing skills to tackle a project like that.   This is a cheaper and easier alternative.   I do have a lightish, good quality tent already (from TiGoat) but the bivy is more for any possible side trips, backup, etc.  

 I plan to test it in all kinds of conditions.  I don't expect it to be condensation free in all conditions, but i do expect it to have much less issues in that area than all the bivy's currently on the market, or at least the ones i read about at BPL and in reviews at different vendors.
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PostIcon Posted on: Nov. 13 2012, 10:46 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Looking forward to your results and experiences.

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PostIcon Posted on: Nov. 14 2012, 12:26 am Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE


(FamilyGuy @ Nov. 13 2012, 7:46 pm)
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Looking forward to your results and experiences.

+1

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PostIcon Posted on: Nov. 14 2012, 1:29 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Thanks guys.
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PostIcon Posted on: Nov. 14 2012, 2:42 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

i'm also interested in how this plays out for you.  i carry a bivy bag in the winter for emergency use - a military surplus gore tex bivy bag.  it only ends up getting used on the rare occasions where i base camp a tent and end up going a little too far out, enough so that i would rather settle in and sleep than try to navigate a trail in the dark.  i have always used it with a well-insulated winter bag rated to -40f.  

military bivy bags are not lightweight or particularly stylish or full-featured.  but, the material is heavyweight and not easily damaged, and the gore tex does allow some moisture to escape.  the bivy invariably collects a layer of frost on the inside of the bag after sleeping in it, even in really cold weather.  because my winter bag has a waterproof outer shell, the frost inside the bivy doesn't really matter.  on one longer trip, i slept inside a VBL bag liner, which completely eliminated evaporative moisture.  that is probably the most utilitarian and results-oriented (if not the most comfortable) way to keep the insulation in your bag intact: waterproof/breathable outer shell, VBL bag liner.


if i were building a bivy, i would take a 2 component approach.  for the bottom layer, the one facing the ground, i would use silnylon or something similar - inexpensive, reliably waterproof, non-breathable.  your sleeping pad doesn't allow vapor to escape anyway, and the pressure of your body against the ground could conceivably compromise a waterproof/breathable membrane against the ground or snow, though that has not been my experience.  i just don't see any reason to spend a lot of money trying to have the waterproof ground layer vent moisture.  so, i would limit the waterproof/breathable fabric to the top layer.  i would also build in a half-zip opening, preferably on one side, with a simple storm flap to cover the zipper.  finally, i would make sure the fabric around the face area does a decent job closing to the point that you (a) have your face exposed to the outside air but (b) don't expose any significant part of your sleeping bag.  finally, i would seal the seams - only way i have ever done that is seam-sealer in a tube; i'm not sure if there are non-commercial seam tape applications.
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PostIcon Posted on: Nov. 15 2012, 1:42 pm Skip to the previous post in this topic.  Ignore posts   QUOTE

Thank you for the feedback Leadbelly2550, some good points you made.  Interesting about the VBL bag--i would have to think about that.

 I'm using heavy coated oxford with a lot of urethane coating on it as the ground cloth/bottom, so should be uber waterproof and very tough/durable, fairly cheap, but unfortunately a bit heavy.

 What i like about this bivy is that during really hot and buggy weather, i just sleep on top of the breathable, water resistant fabric and have the full no-see-um netting on top, so i get maximum aeration.  

But when it's colder, rainy, or snowy, i just flip it over on top of me, and i'll be either inside the bug netting or not.  I get your point about having as much of the sleeping bag covered as possible--most of it should be covered in this case...but the sleeping bag i have for the bivy has WPB fabric just at the head and the feet area, so if some is a bit exposed, this should help a bit.  

 I've decided to not sew/attach the WP bottom to the WPB top so i can get more air flow and flexibility.  Re: seams, not sure about the tape but you can use silicon caulking and mix it with a little mineral spirits and use that to seal seams especially if you're using silnylon.  That's what i did for my TiGoat tent to seal the seems on it (what they recommend on their site).
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