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MYOG Pertex Quantum - Cuben Fiber Bivy
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Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
MYOG Pertex Quantum - Cuben Fiber Bivy on 09/07/2006 22:26:33 MDT Print View

MYOG Pertex Quantum - Cuben Fiber Bivy
Part 1.

Using the dimensions of my "Bozeman Mountain Works Vapr Bivy Sack (Pertex Quantum) size Long, I am making one out of Pertex Quantum and Cuben Fiber.

My Bivy is full size as I have not tried to downsize the dimensions for this project. I will not have zippers or bug netting like my BMW Vapr Bivy has. I will use a draw cord at the lower opening like I think Ryan did on his modified NANO Bivy.

Weight so far:

Pertex Quantum - 2.32 ounces
Cuben Fiber - 0.86 ounces

These weights may go down after sewing and trimming. I left extra material at the top end as I don't know how much extra I might need to sew a box like end at both the top and bottom. I will practice making a box end on a few small stuff sacks before I sew the Bivy.

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Pertex Quantum-Cuben Fiber Bivy-Pt-2 on 09/08/2006 16:35:53 MDT Print View

Pertex Quantum - Cuben Fiber Bivy - Part 2

I began sewing my Bivy this afternoon. I have the draw cord sewn into the neck opening and have sewed the lower two pieces together. The "box" end wasn't as hard as I thought it might be. The top part should be sewn in this evening and that will finish the Bivy.

The weight of the Bivy as you see it is 2.68 ounces.

I am going to use Cuben for the small top piece and that should give me a finished Bivy at or just under 3 ounces. If the Cuben doesn't work after a good test I will cut it off and replace it with more Pertex Quantum.

R Alsborg
(FastWalker) - MLife

Locale: Southwest
Re: MYOG Pertex Quantum - Cuben Fiber Bivy on 09/08/2006 17:03:09 MDT Print View


Aren’t you concerned about the durability of cuban fiber especially for a bivy floor?

kevin davidson
(kdesign) - F

Locale: Mythical State of Jefferson
Bill's bivy on 09/08/2006 17:34:28 MDT Print View

Except in the area of puncture resistance, Cuben is a pretty tough material. I would be even more concerned about subbing in more area of the bivy in Cuben (to save weight) at the expense of breathable material--- condensation city. I would use the pertex on top and sides and very generously in the hood area. MLD has a very good idea to ventilate and reduce condensation--- a drawstring foot opening---I use this feature a lot. Finally, I would taper the bivy towards the foot--- this would save a few grams in an area which for most people, doesn't require a square cut---unless you plan to use this w/ a non-tapered sleeping bag or quilt.

Edited by kdesign on 09/08/2006 17:39:32 MDT.

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Pertex Quantum-Cuben Fiber Bivy on 09/08/2006 17:36:28 MDT Print View

Hi Roger,

Question - "Aren’t you concerned about the durability of cuban fiber especially for a bivy floor?"

Answer - No,
I will still use a light ground cloth and the Cuben Fiber is stronger than most of what is used for the bottom of really light Bivies. Nothing is puncher proof. Check out the NANO Bivy here. I am real sure it is some Cuben product. I expect the same one I am using.

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Pertex Quantum-Cuben Fiber Bivy on 09/08/2006 17:52:53 MDT Print View

Hi Kevin,

This Bivy is for my Oct hike and I just needed to get it done. It is just a little smaller than my BMW Bivy. I will be using this one in cold weather to help extend the range of my "stay warm" stuff. It is also a part of my stay warm system for my Sub 2-lb, Sub 3-lb and Sub 4-lb gear list. I am trying to see how light I can go for a winter gear list and still be warm enough.

I am going to make several more and have a number of design ideas. The drawstring foot opening is part of one of them. I think I have read about you doing this and believe it is a good idea for warmer/rainy weather.

I am going to try Cuben for the hood area on this one and see how that works. If I don't like it I can cut it off and replace it with more P-Quantum.

I have been inside the Bivy and the size is about as small as I can go for my size and height and get my quilt and/or sleeping bag into it.

Adam Kilpatrick
(oysters) - MLife

Locale: South Australia
Re: Pertex Quantum-Cuben Fiber Bivy on 09/08/2006 21:13:11 MDT Print View

The bivy looks awesome already bill!

When you get the time later on, will you trim it down further to save on weight? If so, or if you did, how low do you think it would go?

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Pertex Quantum-Cuben Fiber Bivy on 09/08/2006 23:05:36 MDT Print View

Hi Adam,

Thanks for the nice comment.

This one really has nothing extra except for its size and maybe the draw cord and mini-cord lock which weigh 2.7 grams.

I need to be able to use this Bivy in colder weather. If I made it any smaller I don't think it would work with a quilt or sleeping bag. I have been in it of it and it is not to big for me.

I am going to make a summer bivy that should be smaller and lighter than this one. I might be able to make the summer bivy in the 2.5 ounce range. If I used all Cuben I could easily get under 2 ounces. With the Cuben I think I would have to be able to vent it like a tube tent or I might drown in it.

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Pertex Quantum-Cuben Fiber Bivy-Finished on 09/08/2006 23:21:19 MDT Print View

My Pertex Quantum / Cuben Fiber Bivy is finished. It weighs 2.82 ounces.

A few pictures of what I have been doing today:

Adding the Draw Cord and Mini-Cord lock

Cutting the Cuben Fiber:

Sewing the last seam:

Finished Bivy:

Bivy with a long balloon to hold the hood up.

Folded size - 4" by 4.5" by about 1.5" - book for scale.

(jhaura) - F

Locale: Trail
Nice Job Bill! on 09/09/2006 00:03:48 MDT Print View

Is the drawcord only on the bottom end of the top and not on the cuben hood? If so, what is your strategy for keeping wind blown dirt, sand and bugs out? It must cinch up around your chest I guess, but this still leaves the hood section vulnerable.

I go with my two dogs and after two or three creature chases during the night my bivy is covered with sand and dirt, so I appreciate a tight seal.

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Pertex Quantum-Cuben Fiber Bivy-Finished on 09/09/2006 00:53:30 MDT Print View

I sewed a placed for a draw cord in the front of the Cuben hood but will try it without first. I just wasn't sure I wanted to be that closed up inside the Bivy. I liked the idea with the balloon to keep the hood away from my face/head area but still close over me if I wanted to do that. I also played with a wire to make a hoop of sorts to do the same thing the balloon does. I have an OR Advanced Bivy that uses two hoops in the hood part. It is Gore-Tex and you could sleep out in rain with it and stay dry inside. Getting out in the rain was another story. I went to a small tarp like thing to cover the top 1/3 of my body.

I have several ideas for a hybrid sort of bivy that I want to make for next years Spring rains. If any of the ideas work I will be able to give up the tarp and save a few ounces.

The cord on the lower part of the bivy hits me about at my neck line.

Remember this bivy is for cold weather and if necessary I have a BMW bug net.

Edited by bfornshell on 09/09/2006 00:55:18 MDT.

Einstein X
(EinsteinX) - F

Locale: The Netherlands
When? on 09/09/2006 05:42:40 MDT Print View

Hey Bill,

I'm still amazed every time you post a new project. Being lazy as i am and not having a sewing machine yet :(, when can we start buying "Bill Fornshell gear"??? :D

Keep up the good work and good luck on these and more projects,


Eric Noble
(ericnoble) - MLife

Locale: Colorado Rockies
Re: Pertex Quantum-Cuben Fiber Bivy-Finished on 09/09/2006 08:15:56 MDT Print View

Bill, did you use any 3M tape on the seams? What kind of thread do you use with the Cuben, and about how big are your stitches? It has been a real joy following your projects. Thanks for sharing!

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Pertex Quantum-Cuben Fiber Bivy-Finished on 09/09/2006 09:19:23 MDT Print View

Hi Eric,

I have the 3M tape and have used it on small things. I think it is a lot of trouble on a long length. For me to use it more I would want a second set of hands. The sail makers use a special "Hot Glue" gun and special glue. One of those would make big things much easier and I would expect a better seam. The special Hot Glue gun is about $1600 and then you have to buy the glue and gun cleaner stuff. To much money for me just doing a few things for myself.

Before I start with a new fabric such as with the Pertex Quantum or when I am sewing two very different types of fabric I play a lot with scrap. I run a lot of different combinations of stitch length and stitch width. I am learning as I go but my seams are looking much better than my first sewed items. For the standard I look at my G6 and the BMW gear I have. I would like to be able to watch the sewing part of who ever makes their gear.

I use Gutermann Thread from Quest Outfitters and good needles. I ended up with a stitch length of 2 and a stitch width of 2 on the Bivy. Sewing machines are different and you need to do some testing to see what you machine setting might need to be.

To Einstein X:

There are several problems with making and selling something like SUL Gear.
1. Getting the really good, light weight fabric for me would be very hard. I was very lucky when I was able to get 10 yards of Pertex Quantum 2 years ago and that may never happen again.
2. Really light stuff isn't very strong and if I was selling anything I would not "warranty" it past your door-step.
3. My sewing skill may not be up to it yet, if ever. Making gear for myself is one thing, making it to sell is a much bigger issue.
3. Time to do it. I am slow and have some other things I want to do before I get much older.
4. Having said all that, things have a habit of changing so you never know.


Locale: Pacific Northwet
Re: Pertex Quantum-Cuben Fiber Bivy-Finished on 09/09/2006 10:03:57 MDT Print View

Hi Bill,

Great job on that Bivy. It packs down really small!

What are you using to hold up the head end? Is that a balloon? It looks really clever, I like how it gives structure to the head end of the bivy.



(jhaura) - F

Locale: Trail
Bivy Design Alternative on 09/09/2006 10:16:17 MDT Print View


I've been using this Quilt Bivy design for some time now and really love the versatility/simplicity.

When the ground is not nice duff, I have a nylon balaclava type hood which works as a ground protector and pillow holder. I love it because I can switch positions and the hood and I both rotate in the bivy while the bivy stays in place. It really feels spacious and open.

Really it is very similar to your current design but has a removable smaller hood. In your materials I bet you could save a few grams.

Anyway just offering a little fodder for your future brainstorming on designs. If anyone can come up with a better bivy design you can!

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Pertex Quantum-Cuben Fiber Bivy-Finished on 09/09/2006 11:14:00 MDT Print View

Hi Daniel. Thanks.

Yes, the bivy will pack down really small. I may get to the point that I don't need much of a pack.

You are correct that I am using a balloon. I have a lot of balloons and had these 1" x 60" little guys. They only weigh 1.1 gram each. The only bad thing about them is I need my 1.75 ounce balloon pump to blow them up. I tried blowing them up by mouth and can't get them started. I have tried blowing them up with the pump first and then blowing them up by mouth. I can do that but not easy. I may have to blow them up a couple of times to break them in some. I don't want to carry the balloon pump just to blow up one balloon each night.

I am working on a couple more ideas for balloons and if any of them work I would need the pump. The pump is modified from a starting weight of 2.8 ounces down to it current weight of 1.75 ounces.

The balloons look a little funny but they work, they pack to about nothing, they weigh about nothing, they are cheap and I can recycle the used ones into "finger" sling shots and have fun shooting at shelter mice.

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Pertex Quantum-Cuben Fiber Bivy-Finished on 09/09/2006 12:02:32 MDT Print View

Your design is fine. We always have something we can lay our head on to keep it "out of the drit".
"Weight: 5.8 oz (in silnylon, imagine how light in spin or cuben?"
For your size bivy I figure you used about 2.08 sq yards of material for each the top and bottom.

Using a really good material for the top with a true weight of about 1 ounce per sq yard and Cuben for the bottom the material a Bivy like yours needs about 2.61+/- ounces of fabric.

The really big difference will be in the cost.

Top - Momentum 90 (about a true weight of 1 to 1.1 ounce per sq yard) from Thru-Hiker at $11.95 a yard (need two yards with a seam or 3 yards without a seam). Cost with shipping maybe $30 - $42.
Bottom - Cuben ( about a true weight about .35 to .44 ounce a yard) (need three yards) from Cuben Corp at about $17 a yard. Cost with shipping maybe $51.

Total $81- $93 for a bivy that weighs about 2.65 ounces with a cost per ounce of about $31 - $35 an ounce.

If you got lucky at Wal Mart the material for a bivy this size (5 yards) might cost you less than $6.

Cost of Wal Mart bivy maybe $6 and a weight of maybe 6 to 8 ounces with a cost per ounce of about $.80 an ounce.

A 2.65 ounce bivy is below the SUL catagory and I don't think it will ever be cheap to get there.

Eric Noble
(ericnoble) - MLife

Locale: Colorado Rockies
Re: Pertex Quantum-Cuben Fiber Bivy-Finished on 09/09/2006 13:37:32 MDT Print View

Bill, I guy I used to juggle with also made balloon animals, and such. There is a secret to blowing them up without a pump, though it is still difficult. Stretch the balloon out really good before you start, and pull on the balloon as you blow. Your eyes will still just about pop out. I don't know how my friend didn't end up looking like Marty Feldman :).

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Pertex Quantum-Cuben Fiber Bivy-Finished on 09/09/2006 15:10:26 MDT Print View

I have tried all your suggestions and I am still popping all my blood vessels. No luck blowing up the 1" balloons by mouth.

Then I tried to blow up some 2" ones I have without a pre-pump. I can blow up the 2" balloons. The 2" ones are a few from a sample. I called my local balloon man and he sells the 2" by ?? 100 to a bag. I will get a couple bags to play with.

The 2" balloons I have weigh 1.2 grams /0.04 oz.