Bivy Material Suggestions???

Generic Goretex might be a little heavy on top.

FWIW, I sewed two bivy sacks about thirty years ago using Goretex on the top, and coated nylon on the bottom. They work fine, but they are heavy.

–B.G.–

I use 1.4 oz silnylon from thru-hiker.com. Richard recommended it as the only waterproof silnylon. I've found it to be waterproof. It was a little slippery, then I put some blobs of mineral spirits:silicone maybe 10:1.

I use eVent for top which is maybe slightly better than generic goretex. Only thing is it's kind of heavy.

I have some M50 for my next version, 0.7 oz, not nearly as waterproof, but I only want it to be resistant to occasional drops from rain splash or wherever. Or frost or dew.

Just depends whether you want lighter weight or more water proofness.

How does the Hi-Vent compare to the E-Vent?

Probably eVent is a little better, but it is not available. If I was to do a WPB right now I'de use the 1.8 oz Hi-Vent, but I have no experience with it. Maybe someone else does. Quest has good stuff so it's probably good.

Do you want to use bivy in the rain, or under tarp?

Jerry:

My intent would be to use it under a tarp. However, being lazy, I'm sure I'd just use it by itself if I didn't think it was going to rain.

"Do you want to use bivy in the rain, or under tarp?"

That is the important question.

If it will be used directly out in the rain, then you need a fairly high degree of waterproofness. If it will be used underneath a tarp, then you need just a bit of splashproofness.

My idea, not yet proven out, was to use a lot of mesh in the top for maximum breathability. Then add a "rain flap" which would cover over the mesh, just for a rain storm. The mesh would still allow a bit of breathability under the rain flap.

The rain flap could be made out of cuben fiber, for minimum weight, or out of silnylon for less cost.

–B.G.–

Then maybe one of those 0.7 oz fabrics like M50 would be better.

I'm just saying, because I used WPB, but now I'm thinking I should have used M50 instead. If you use 3 yd2, and it weighs 1.8 oz/yd2 instead of 0.7 oz/yd2, then we're talking 3.3 extra oz, if that's important to you.

Bob & Jerry thank you so much for your replies. I really appreciate your insight.

I've made two versions of the Lytw8 bivy and for the uses you describe I think that's the bivy you're looking for.

M90 upper with Sil bottom for my first version … works like a charm. It can be a little bit slippery if you're using an inflatable pad but foam pads don't seem to move around much.

Second version was M55 upper / .51 Cuben bottom and extended zipper for easier entry exit. I LOVE this bivy and it works incredibly well under a tarp. The M55 breathes much better than the M90 while still repelling some drops. If it does get wet, the bivy dries out in all of 15 minutes in the sun. Pretty remarkable.

For more bivy banter… check out this discussion.

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=44617

"HI-Vent is created by applying a polyurethane coating with a special DT print matrix which acts as a dry-touch, half-layer coating"

.polyurethane wpb fabrics are cheep and frequently used. Quest doesn't list any breathability numbers but based on my past research I found polyurethane coatings to have ratings at about half that of gortex. Event has a breathability rating that is higher than gortex and significantly higher than polyurethane.

You might want to consider a Tyvek bivy. Tyvek is considered water resistant but it is more water resistant then M90 or M50 so in a light ran Tyvek should keep you dry without a tarp and it is breathable. Although I haven't found any numbers for breathability so I don't know how it compares to gortex or event.

There are different Tyveks. The HomeWrap is waterproof but not very breathable. Good for the bottom.
The other material I have is much better for the top and can handle rain without tarp :)