Idea for a bivy top material vs eVent.

[Anonymous]

The concept–serious splash and snow protection, at slightly less of the cost and weight (most common forms i can source for MYOG) of eVent and no darn NDWR to worry about. Primarily for winter use, but can be used in all seasons if necessary. How to implement: 1. Take lightweight woven fabric, preferable taffeta, preferably made of polyester and preferably uncoated (sans NDWR). Treat with homemade silicone adhesive/paint thinner slurry 1:10. Provides long lasting and truly DurableWR, as well as hopefully increasing HH some. 2. Take UL nylon fabric, preferably taffeta, but more breathable (preferably uncalandarered) nylon with DWR, sew to above siliconized poly taffeta. If i wasn't lazy, i would siliconize this layer as well (and probably with slightly thinner slurry). The DWR should last awhile being in between two layers, but maybe i'll siliconize this too. 3. The top of the bivy will have cheap, very light nylon Tulle sewn to a good portion of the waterproof ground fabric, which will be the venerable 1.4 oz Silpoly PU4000 fabric. Reinforce the Tulle at the edges. Here is where it gets a little weird. Instead of sewing most of it or using a zipper to attach the above combo of 1 and 2 fabric to the Tulle/Silpoly part, it will only be sewn at the end of the foot area and most of one side. It will be slightly wider than the Tulle/Silpoly part of the bivy on the other side, and on the inside there will be velcro tabs sewn or glued on strategically so that it can be secured for wind. So basically the top material will be a 1.1 oz/yd2 + .67 oz/yd2 + .3 oz/yd2 and with light silicone coating, should weigh a bit above 2.2 oz/yd2, and of course the bottom material–the silpoly will weigh 1.4 oz/yd2. Sans zipper, and custom sized to my smaller frame, i think i can get it down to the weight range of 9 to 10 oz–maybe lighter.

[Jerry Adams]

I have M50 top material. Pretty good compromise between breathability and water proofness. It'll leak in a real rain. 0.7 oz/yd2

[Anonymous]

Yeah, i have some of the older M50 material that's very tightly woven, which i put on the bottom of a quilt for wind protection and/or severe cold conditions. I've heard that in colder weather single layer bivy's tend to build up condensation on the inside of the top material because of where the water vapor tends to condense most often? I was looking to avoid that, and have some serious WR if needed. I like to cowboy camp when i can, so i was looking for something that could handle some rain for a little while till a tarp/tent is set up. Or something that can handle being in a snow trench (doing many Snow Dance Rituals this year). Do you think that M50 could handle snow trench conditions?

[Jerry Adams]

I try not to camp in the snow so I have no experience. But there'd be no rain drops falling on you which is what's a problem for M50. I have a M50 bivy and haven't noticed condensation. Down to 25 F or maybe 20 F.

[Mitchell Ebbott]

Here are the two problems I foresee: 1) IIRC, (N)DWR works based on surface tension. It doesn't operate the same way as waterproof fabrics, and can't be accurately measured by hydrostatic head. If it isn't the outermost layer, drops won't be able to form and roll off, so adding the tulle on top will render your middle layer pretty much useless. 2) I have my doubts about the breathability of that homemade siliconized nylon. Have you tested it?

[Paul Beres]

dave miles of milesgear – maker of the Uber Bivy – sells the fabric he uses for his bivys for $5/yd. 2.3 oz. sq yd so he says. Easier, cheaper, and probably just as light as your scheme.

[Sam Farrington]

Note that WPB rain jackets generally are made of a material with much higher HH than tent or tarp walls. For example, 3000mm is considered a very good HH for a tent or tarp, better than most on the market, but best quality rain shells often go 3-4x higher. Not sure of the reason, but apparently a suspended tent or tarp wall can function effectively with a much lower HH than a garment worn over a moving human body. A bivy top lies somewhere between a tent or tarp wall, and a garment. Hunting around, I was able to order from Europe a 2-3 oz WPB that Roger Caffin tested with an HH well above 3000mm. Unfortunately, could not obtain any info on the vapor permeability. Because not all of a bivy functions like a garment, I would want a higher VP than a garment to avoid soaking condensation. This is because WPB garments work by the pressure of humidity on fabric next to the body. But not all of a bivy will be next to the body. The posts focus on winter conditions and situations with minimal rainfall. That does not apply to 3 season camping in Northern New England and Colorado, where I have often experienced long deluges during the night. For those areas, I would want a bivy with both high HH AND VP, knowing that there would be periods of long exposure to drenching rain. Certainly I would try Paul Mclaughin's source before relying on MYOG slurries. Richard Nisley tested one of them and it did poorly. He has also tested a number of fabrics with only Durable Water Repellent treatments. They all had poor water resistance (HH). Paul's suggested source might provide something workable in winter, at a low $ cost to find out.

[Franco Darioli]

"Not sure of the reason, but apparently a suspended tent or tarp wall can function effectively with a much lower HH than a garment worn over a moving human body." Capillary action, or for tents lack of capillary action. That is why some tents with poles on the inside will leak first by those poles or, when you touched a cotton fly, it then started to leak from that spot.

[Jerry Adams]

I made a micro tarp out of polyester DWR Same thing, not too bad until I touched the inside, then it started leaking especially, if the sleeping bag made continuous contact

[Anonymous]

Hi Mitchell, The tulle would be the innermost layer–not an outer layer. There would be at least one siliconized layer over that, and possibly two (depending on how lazy or not i am). I've added silicone coatings to various fabrics. If they are sufficiently air permeable to begin with, they remain air permeable, but with decreased air permeability. Which in the case of a cheap, Costco sourced windjacket i treated, was an improvement. Original CFM was way above what a windjacket should be. Adding the silicone coating brought it down to a more ideal range (i would guestimate in the 45 to 55 CFM range).

[Anonymous]

Hi Paul, I'm not sure, but doesn't Dave M. use a fabric that is similar to Frog Toggs? If so, i would like something more durable and air permeable. Frog Toggs has CFM of .33–a bit below eVent. Even thin, UL woven nylons are more durable and stronger than non wovens such as Frog Toggs.

[Anonymous]

Hi Sam, I would bring a tarp or tent in conjunction with the bivy, so i only need as much protection as it would take for me to set same up in rain. In other words a relative few minutes or so. "Certainly I would try Paul Mclaughin's source before relying on MYOG slurries. Richard Nisley tested one of them and it did poorly." Are you referring to the Maxima ESD fabric that i sent to Nisley to be tested? The problem with the Maxima fabric was that i didn't know it had an original DWR until Nisley tested it. Neither the place i bought it from, nor the corporate literature i read about it, mentioned a DWR specifically. As it's basically made for hospital clothing, i assumed it probably didn't have one. So, unlike fabrics that i know have a DWR, i did not pre treat it to wash same out (i've done this with other fabrics–i use a couple long hot water wash cycles with oxy clean and then rinse very well). So, when the silicone coating was applied to the fabric, it was applied to the DWR and not directly to the fabric. Hence, it could not and did not bond with the fabric. The surface energy of some other DWR's are actually even lower than that of silicone. This explains the poor results of the test. Because the silicone wasn't bonded directly to the fabric, as soon as the water pressure built up, it got blasted off, not increasing the HH at all from the original (though it did decrease the CFM from 10 to 1). I'm fully confident that had i known it had a DWR already, and took it off beforehand, that the silicone treatment would have increased the HH AND also have added a truly durable water resistant coating. Durable, mostly only because it's much thicker than most other DWR coatings. As mentioned earlier to Mitchell, i've treated various fabrics and articles of clothing in this manner, and it has helped improve water resistance of some of them for simple before and after tests (like running under a sink).

[R]

Pertex Shield, avail: http://thru-hiker.com/materials/coated.php Waterproof – 10,000 mm Breathability (MVTR) – 7,000g* 2.5 layer Actual tested finished weight: 1.8 oz/yd2 (63 g/m2) $16.95 / 57" roll yard. Same ballpark cost/weight as your suggested home-brew: 2x 1oz/$7 fabric + treatment supplies. Used in the OR Helium Bivy.

[Anonymous]

There's a couple issues with Pertex Shield Rene. One, the PU coating is on the inside, but the DWR on the outside is a traditional one, hence is not truly durable. Once that comes off, the breathablity goes down. Two, it's not that breathable to begin with even with a brand new DWR. I want/need a fabric that has a truly durable water resistant outer coating, and much higher air permeability. Crucial in winter time, when water vapor can actually freeze within and stop up a membrane and thus really decrease the ability for it to move moisture.

[R]

What are you target/min/max values for HH, MVTR and CFM?

[Jerry Adams]

Pertex Shield is good as a rain jacket where you need to be rain proof Or if you wanted a rain proof bivy If you wanted a splash and dew proof bivy, maybe Pertex Endurance

[Anonymous]

I'm looking for a total HH ranging from 900mm to 1200mm or so, and CFM of around 3 to 5. MVTR need not be considered, because once you have a measurable CFM, you have a much higher MVTR automatically. I believe the above can only be achieved with a double layer of materials. One outer layer to slow down initial force of rain and the other to maintain water resistance. (more and more, i lean to having both layers treated with a silicone coating, but one with a lighter coating). The question i have, is should the lower CFM and higher HH fabric be the outside layer or the inside layer? I'm leaning to it being the 2nd, inner layer (see last part of below paragraph for reasons why). Technically, it will be a 3 layer, since the tulle will be the innermost fabric and be between the quilt and the 2nd layer of water resistant material. There are single layer, EPIC fabrics that come close to the above specifications, but back when i was a M member, i remember reading an article which indicated that EPIC could have issues in the winter and in more extreme cold when it was being used for applications like bivies and tents where body heat wasn't enough to keep the material warm enough and water vapor froze inside the fiber interstices.

[Jerry Adams]

my experience with EPIC, and what I remember other people experienced, was that it was more water proof, then it gets contaminated with dirt or dust or whatever, then it's not so waterproof your specs are for new fabric

[Anonymous]

"my experience with EPIC, and what I remember other people experienced, was that it was more water proof, then it gets contaminated with dirt or dust or whatever, then it's not so waterproof" Yes, but the beauty of EPIC according to Nisley is that it can be field cleaned and maintained to bring back water resistance. This is apparently why the US military uses it a lot. Also, consider that if i siliconize both layers of fabric, then the inner layer will stay cleaner much longer, so that even if the outer layer does start to wet out from dirt or what not, the inner layer will still provide adequate water resistance. "your specs are for new fabric" Well, not really. The closest analogy is putting together two layers of more air permeable EPIC. There are some EPIC fabrics that approach near 1000 mm HH, but air permeability is lower, like 1 CFM if i remember correctly (i'm assuming that the base fabric they use is very tightly woven). But if you put together say two fabrics with say around 500 mm HH and CFM each of 5 or so each, you should get a bit higher real life HH than the above single layer fabric, while being more air permeable. It's just thinking outside the boxes.

[Jerry Adams]

I think you're onto something about two layers of fabric, like paramo, although it does make it heavier I'll have to try to find my epic jacket and see if I can wash it

[Anonymous]

Well, theoretically i could use two layers of the .67 UL nylon fabrics, which would really cut the weight down. I don't know how much the factory DWR coating adds, but say it's the .07 part (so .6 without the DWR?). Silicone coating would up it probably to .75 or so? So you could get it to around 1.5 oz/yd2, then add the .3 for the netting. Under 2 oz for serious, long lasting, less fussy water resistance doesn't sound bad to me. Granted, if you want a bivy that you don't need a tarp, and you want to be able to subject it to full, heavier rain for longer periods, take an eVent one. Doesn't sound like much fun to me though, to be stuck in a bivy in such conditions. Even if you just bring a mini tarp or tent, makes it a lot better. But like i said, i like to cowboy camp. I did this weekend, low down to around 26 and slightly windy (was suppose to be 32 or so). No rain anywhere near the forecast, so i didn't take a tarp or tent, and i wasn't that far from an AT shelter if it had started to rain.

[Jerry Adams]

Same here, if it's not going to rain no need for tarp. I really like the freedom If it's raining I like mid, because I can sit up, enough room to put some stuff, if I want to cook I'll leave door partially or totally open,… If I don't really have enough insulation for the conditions, especially if it's a clear night, sometimes I'll put the tarp up. It adds some effective warmth.

[Anonymous]

Bought 6 yrds of discounted Membrane10 at RSBTR. Going to try two layers of it with silicone coating. Might not be breathable enough with the silicone coating? I haven't handled this material yet, but it sounds like it is probably pretty tightly woven? I have some left over Argon, which is fairly breathable, so i might use that as one of the layers instead.

[Author]

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