MYOG Bivy; what top material?

questoutfitters.com has some 2.5 oz/yd2 WPB that they said on the phone is pretty waterproof

if you have a tarp that keeps the water off you, you could use 0.9 oz/yd2 from owfinc.com or thru-hiker.com. Or the KG-8D is 0.65 oz/yd2 which is $7/yd – I got some of that but I used it for a lining.

eVent is the best. 1.6 oz/yd2, the best water resistance, but no one sells it.

In my experience, PNW isn't so humid, as it's raining all the frickin' time. In my sleeping bag with WPB shell, it dries out over night from body heat.

What functions do you need from your bivysack? Bug protection, wind protection, dirt
protection, snow protection, rain protection, keep you and your bag or quilt on your pad,
provide extra insulation, hold two people's pads together, keep
extra gear dry, maintain modesty in hot weather, provide a ground sheet etc.?

Does it need to be durable, light, cheap?

Different needs will dictate different materials.

@David: I'm really looking for something that will provide some wind resistance (since I'll be using a tarp), definitely keep the bugs out, and keep additional spray from rain at bay. I'll be experimenting with different size tarps so maybe something a little more cautious on the side of rain resistant would be in order. Also, I will only be using this for spring thru early fall weather.

It seems to me, that momentum is the best way to go (available from thru-hiker). Most people seem to speak very highly of it in terms of wind/spray resistance and breathability and lack of condensation, which would likely be a problem with a full WPB bivy. If you'll be using it in conjunction with a tarp, the momentum will be plenty water resistant.

I used a myog bivy with a momentum 55 top and 0.51oz/sqyd cuben bottom in the sierras last summer. It worked well in high winds and under a 5.5 x 8.5 ft tarp in all night rain.

"It worked well in high winds and under a 5.5 x 8.5 ft tarp in all night rain."

That sounds like great fun.

–B.G.–

I'm going to make a bivy too and bought the materials. I am using owfinc (for all of it) silnylon 2nds for the bottom and .9oz breathable dwr ripstop for the top.
PS. I found a thread where someone tried a polycryo bottom and propore top: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=21902

My MYOG bivy has a sil-nylon bottom tapered toward the feet, 4' to 28"

The bottom three feet of the top of the biviy is covered by momentum-90 as splash protection. The rest of the bivy is mosquito netting using the full 5' width to allow for the netting (and the bugs)to be away from my body in the heat of summer. I also know from experience that the netting definitely blocks some wind and retains heat so I tend to use it year round. I keep meaning to make a sil-nylon bottom momentum 90 top bivy for the shoulder season but as the bug bivy works so well I just don't bother.

Conner, I used owfinc silnylon for bivy bottom

Water sometimes leaks inside

I coated it on the inside with 10:1 mineral spirits:silcone and it was much better

If you find your bottom leaks too much you might want to try that

Would love to find some BD nanosphere. There is propore well under 2 oz, but it won't last very long.

The lightest ever available WPB I've found is Epic Malibu, which varies in weight, but is about 1.85 oz per sq. yd. on the average. No doubt you know there is great controversy over whether it fails in heavy rain, and by how much, especially if contaminated by soil and/or oily substances. Inasmuch as WPB clothing appears to require more water resistant material than tent/tarp walls, a bivy would probably be more like clothing, and Epic treatments have not worked well at all for clothing worn in the rain.

I have some 2.3 oz emerald colored nylon with an off white WPB coating from one of the UK online outlets (maybe Point North – they called it 'pertex,' but of course it is not). Roger tested it, and it is quite WP, though. PM me if you would like a sample. Everything else WPB seems to be 2.5 oz or more.

Jerry,

Where on earth did you find 1.6 oz eVent material, in any form. Please tell me.
I wouldn't kill for it, but almost.

AS FOR THE BOTTOM: The silnylon currently sold by Thru-Hiker is quite waterproof, based on tests by Richard in consultation with Roger and reported on this site. Even my little remaining best quality silnylon manufactured years ago is not as water resistant. The expansion (sag) with temp drops and cold rain or snow is still there, but not so much. Don't see how that would be a problem with a bivy bottom, though. Although it might be too slippery for some – not me who constantly rotates from one side to the other – but don't use a bivy anway, so not an issue.

Even after reading tons of posts, am still trying to decide between the 1.36 oz T-H sil and the thicker mylar 1.26 oz cuben from Zpacks for a tent floor. Certainly the sil will compress and pack better, be quieter, and acquire less sticky gunk. Theoretically, the elasticity of the sil would resist punctures and abrasion better. But that cuben is tough stuff. What to do. The answer would probably affect choice of a bivy bottom, also.

Thanks for the tip Jerry.
-Conner

BPL had some white eVent. Sold a little of it, then dumped the rest to ???, who sold the rest.

Ben Smith of Goosefeet. I think that he sold it all though.

What is left:
http://goosefeet.webs.com/clearance.htm