I am getting ready to build myself a new bivy and can't decide which material I should use. My current bivy is heavy and not that breathable so I want something thats lighter in weight or something that's a similar weight and very breathable.

I usually sleep under some kind of shelter but would love to have a bivy that would let me leave everything home.

My Options;

All Cuben bivy = Super lightweight but a sweat-lodge.

A Silnylon floor with with Pertex Quantum top = lightweight but not very storm worthy

A 70D silicone/pu blend bathtub floor with a 3 layer Gore-Tex ProShell top = heavier then the rest but bombproof.

Any input would be greatly appreciated.

Have you checked if you could buy breathable cuben?

I sewed my own first bivouac sack over 30 years ago. It was too tight. Then the second one had a coated nylon floor and Goretex top. That was much better. Then the third one had a coated nylon floor, Goretex top, bug netting, and it was large enough for two people. Within the last year, I sewed my last one. Coated nylon floor, Momentum top, and a zipper.

Let me try this one for 10 or 20 years, and then I will do another one.

--B.G.--

Hey Eugene,

I thought about it and even considered building a production run of them so I contacted Cuben Tech about the material but was told it's not available yet and was still in testing.

I have a feeling the breathable stuff is gong to make the standard cuben look cheap.. Most WPB materials use some kind of fuseable web or dot matrix adhesive to join the face material and film. But those methods of construction won't work with cuben fiber so I would imagine you would have a classic catch 22. The better the film bond the worse the breath-ability.

As of now, unless it's as breathable as eVent, cost the same as standard cuben and weighs under 1.5oz it won't interest me. Mainly because cuben is already way overpriced and has some serious downfall's.

Hey Bob,

Of all your bivy's which one do you like the best? Do you use the Momentum one without a shelter? If so how does it compare to your Gore-Tex one?

Thanks,
Lawson

I have used a silnylon floor bivy for years.

It wets through when it's real wet.

I coated inside with 3:1 mineral spirits silicone caulk and it's lasted for many trips and is much more waterproof.

"Of all your bivy's which one do you like the best? Do you use the Momentum one without a shelter? If so how does it compare to your Gore-Tex one?"

Hmmm. Hard to answer. First of all, the whole reason for my first sack (c. 1978) was the result of a traumatic experience on Mount Rainier with a totally saturated down sleeping bag. As they say, we learn best when we learn the hard way.

Goretex is a much heavier top fabric. As a result, I think I feel warmer inside those sacks. For a cool winter night, that works. I use these a lot for car camping when I am too lazy to put up a tent, but often I sleep on top of them rather than inside them. Back when I made these, there was no other game than Goretex. One is 1.5 and one is 2.0 pounds. By modern standards, those are a little heavy.

The newest one with Momentum is OK. I had designed it to be fairly light (I would have to double-check, but I think it is about 8 oz.). I had made it specifically to use in summer in Alaska, so I intended it more for light rain and humidity. I have no idea how it would be for heavy rain for a week. Also, it was done as a skill test. I bought my sewing machine only last December.

So, for a light and fast solo summer backpack trip in Yosemite, I would take the 8 oz. Momentum. For the same with one buddy, I would take only a shelter. For the same, except during rainy season, I would take the shelter plus Momentum.

--B.G.--

Momentum is not remotely waterproof, just slightly water resistant... which I mention because there's next to no comparison to a totally waterproof/B fabric like Goretex. Two different applications...

Brad, I won't argue the last sentence of your statement at all. However, I will contest the idea that it's only "slightly water resistant". The stuff is extremely water "resistant". Especially in areas without stitch work. Waterproof? No, not at all, although the term is subjective, technically, the WP/B fabrics that have a measured water pressure failure point without bursting the fabric open are also only "water resistant" no?


The tight weave and quality DWR of "Momentum" and "Intrepid" is such that it can hold significant water without leaking. More than many low quality sil's can.

The momentum is a good choice for alot of applications but I have decided to use the Gortex 3 layer with a 70d coated floor. I think the additional weight will be a wash since I will use the bivy bag as a stand alone shelter.

I have never owned a bivy with a draw cord so now I am debating zipper vs draw cord.

Any suggestions?

A draw cord might be easier to sew in. For my first ones, I used grommets and had the draw cord run in and out of those. That's pretty foolproof, but not elegant.

A zipper is a little more elegant, but there are all sorts of orientations to consider. With some orientations, you may try to open it from the inside, and it would snag. I coated the soft part of the zipper tape with seamsealer to improve its waterproof nature. Eventually, you end up with a zipper that is too heavy, which defeats the whole thing.

I suppose that Velcro is another possibility.

I don't think that Goretex fabric will be a problem, especially for cold or wet use.

--B.G.--

Thanks for the input. Zippers configurations can make your head spin, so the draw-cord would make things much more simple. I have never owned a draw cord bivy because I was always concerned they weren't as weather resistant. Florida doesn't get much cold weather but we do get alot of rain and have high humidity year round so I think the Gortex is going to work great. I think I am going to add some no-see-um mesh that velcro's on the inside that way the bivy is a little more versatile on buggy nights.

On a final note...I was pricing materials and it looks like its not going to cost much more to build an extra one so I think I am going to build two at the same time. Maybe I will keep it for a friend, give it away for a Christmas present or sell it on BPL. I guess we will see..

Edited by Mountainfitter on 10/13/2010 15:35:49 MDT.

"I think I am going to add some no-see-um mesh that velcro's on the inside that way the bivy is a little more versatile on buggy nights."

Obviously you want to sew in the mesh so that you can use it or not use it, just depending on the conditions.

I sewed in my mesh to the far top end of the sack, which is actually the head end of the bottom layer. I leave the mesh rolled up and tied, or else unrolled and spread toward the foot end.

--B.G.--

Javan, your comment re:Momentum: "Waterproof? No, not at all" was exactly my point. It is not waterproof, nor is it intended to be. WPB fabrics are.

Yes, I've made many things w/Momentum and am quite familiar w/it. I would not send somebody out into several days of rain having told them that Momentum is waterproof. That borders on irresponsible.