View Full Version : 100% wp/b fabric, wp zippers
Just Jeff
01-14-2006, 14:07
Hey all,
I thought it was discussed here recently, but I went back through the forum and didn't find what I was looking for...so here's a question:
What material is 100% waterproof, and reasonably breathable, to use for a bivy sack. Lightweight is good but not critical - completely waterproof is more important.
I've looked at a few online sources, and some claim a material is waterproof while others claim that same material is "highly water resistant" or has "superb water resistance"...not quite waterproof. I want something that'll stand up to being used as a stand-alone shelter in high winds, but won't drown me in condensation.
Same thing for waterproof zippers - anyone have any experience with these? Are they really waterproof when the wind picks up? I'm trying to avoid sewing a storm flap because the wind will just blow under it anyway.
Any advice?
TIA...Jeff
First, I am not an expert on zippers. That said, the zippers on my backpack look like the ones on my husband's drysuit and they keep out the water very well. As to the breathability of the cloth--well--it seems that truly water proof would cause a condensation problem. Perhaps use sil-nylon then if the weather will be really rainy, tarp over. Others will probably be able to provide better advice.
Nightwalker
01-14-2006, 15:55
What material is 100% waterproof, and reasonably breathable, to use for a bivy sack. Lightweight is good but not critical - completely waterproof is more important.
I don't think that it exists!
Frolicking Dinosaurs
01-15-2006, 06:00
In my experience, you need to provide some ventilation for condensation to evaporate in any totally waterproof shelter to avoid being drowned in condensation. As for totally waterproof fabrics, nylon or polyester fabric coated with a waterproofing material - sil-nylon is the lightest, but some say you get 'mist' through it in really heavy rain. I use urethane coated nylon and have never had a problem.
As for zippers, the material on this site http://www.tizip.com/index.htm explains the different zippers available and the level of water resistance of each. I have not used zippers from this site, but they do a great job of explaining what is available.
I suggest you design your shelter to allow for you to ventilate in heavy wind and rain and that you use storm flaps over zippers to assure you and your sleeping gear / clothing stay dry.
peter_pan
01-15-2006, 09:52
Jeff,
This is a no brainer... IMHO.
Use Microporous Polypropelene ( Same as our JRB Weather Shields, Dri Ducks, Rainwear by O2 Rainshield)....This stuff is totally waterproof, windproof and the most highly breathable available. It is also light at 1.75 oz per sq yd.
The Three draw backs are.... First, it is fragile ( use as the top of a bivi should be fine, field repairs fine with duck tape if one gets a tear)...Second, since regular seam sealer will not hold on it and heat and pressure interlocking seam makers are commerrcial machines ( read big bucks) are not available, an application of this type would have to use overlapping felled seams or false french felled seam and be sealed from the inside on the silnyl bottom of the seam... Third, MP is not available commercially at the retail level.
Given the seam design constraints above.... I would recommend the entrance be designed on the side as an overlapping flap ( 1 inch is fine) using omni-tape, then water proof the under side silnyl with silicone sealer ( Mc Nett)behind the inside piece of omni-tape.
BTW, some one purchased a JRB WS top for the material to make a project such as this about two months ago... no feedback on the project...perhaps he'll see this and post some feedback.
Hope this helps.
Pan
Whistler
01-15-2006, 10:28
The top wpb fabrics that come to my mind are Micropore [and similar], eVent, Entrant DT, Gore-Tex Paclite/ XCR.
Not too sure on sourcing. You might want to check with Dave Olsen at Oware; I believe he keeps a good bit of scraps and raw fabric for sale.
-Mark
Just Jeff
01-15-2006, 12:06
Thanks for the ideas, all. Keep 'em coming!
Dino, bivies don't really have "ventilation" except for the entrance - that's why I need breathable fabric instead of sil. Thanks for the zipper link...I'll definitely check that out.
Pan, I thought about the MP but sourcing is the biggest problem. Since I can't get it in a continuous 9' length that means extra seams...weight, complexity, points of failure, etc. I also wondered if it'll be sturdy enough as a hammock bivy in a storm when it's getting buffeted by strong winds. And thanks for the note about seamsealing...wasn't aware of that. I'd like to find a way for it to work, though.
"BTW, some one purchased a JRB WS top for the material to make a project such as this about two months ago... no feedback on the project...perhaps he'll see this and post some feedback.
Hope this helps.
Pan"
hah, ya small world us light backpackers are... that was me Pan, I'm currently 83% done with the project, so far so good, the stuff is very fragile...i even messed up a small section of the top being careless with tape, 8-12 stiches per inch is a good recomendation (as recomended by Pan) I'll report back when im done with the project hopefully in 2 days or so.
mike!
Just Jeff
01-21-2006, 11:16
Mike,
Could you provide more details about your project? Is it a bivy, a hammock bivy, etc? Any details on the design you'd share?
Thanks,
Jeff
"Mike,
Could you provide more details about your project? Is it a bivy, a hammock bivy, etc? Any details on the design you'd share?
Thanks,
Jeff"
ya, its just the Meteor Bivy from six moon designs.
" http://sixmoondesigns.com/ultralight/myo_Meteor.asp "
should be a nice companion under a poncho or in a shelter on the AT.
the full size pattern was a litttle time consuming, but after that its all easy.
i do have a question about zipper coil, whats the deal with a zipper wedge? i didnt add one, but the thru-hiker.com directions said that a zipper wedge reduces bulk? how can adding fabric to a zipper reduce bulk....
thanks!
mike!
Not sure if this will help, but as I posted it on one of the other threads because the fabric is on sale. If you use anything 100% waterproof you are gonna be soaked in condensation - it's the design of the bivy, your body just gives off to much heat that will be retained in anything 100% WP - it needs to be breathable. You can always check it out
http://www.featheredfriends.com/retail_store/Sale/Fabric.htm