Cuben Fiber - Pertex Quantum Bivy

Cuben Fiber - Pertex Quantum Bivy
Made - 09/07/2006

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.





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.





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.

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.

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.



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.

I was asked about using tape for the seams:
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.

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.






I used CTO.3k.08 on the floor and hood. I think the product numbers have changed but not the web site yet. The weight of the CTO.3k.08 is the 0.33 to 0.35 oz per sq yard.

I thought about using a balloon to hold the hood open and away from my face. Sort of like a little tent with a big door. I have learned how to blow up a balloon so I don't need a balloon pump. I also learned how to tie a slip knot so I can untie the balloon easy and use it more than one time. The balloons weight less than 3 grams each ( I found some stronger balloons) and for a hike with a resupply schedule of 3 to 5 days I would only need to carry one balloon for the Bivy. If I am using my home made balloon bed the balloons are the same size so I will always have a couple of extra balloons if I break one.

The Pertex Quantum is also 3 times heavier than the Cuben fiber. I think we fuss way to much about condensation but If condensation becomes to big a problem on a given night I can push the hood back and out of the way.

Testing will see if this works. If it doesn't work I can always cut the Cuben hood off and replace it with Pertex Quantum.

I have an old OR Advanced Bivy that uses 2 hoop poles. The system had worked very well for me but the poles were to heavy for this Bivy. I had a long piece of Ti wire like BMW sells but just longer. The Ti wire was border-line to light for the Pertex Quantum hood. That was another reason I went with the Cuben Hood. I had been playing with the small balloons for a different project and thought try the balloon for the hood. A balloon worked well and held the hood up really nice.

I am working out the details for version 2 of the Bivy. It will be designed for use in rain and maybe even snow and will not require a tarp. It may be heavier than this Bivy but lighter than a Bivy and a Tarp used together. It is looking more like a baby solo tent when set up. Using a really good and light WPB fabric, Cuben fabric and a couple of balloons or something that inflates I hope to stay well under 5 ounces.

If this new Bivy design works in snow then I can use the weight saved for more insulation in another Quilt/Sleeping something and maybe get a Sub 2 or 3-lb gear list that will work below 32 degrees or maybe lower.

The person I buy my balloons from I have a friend earns a little extra money by dressing up like a clown and doing parties. I called him about getting some balloons and went to pick them up yesterday. He said not many people can blow up the small ones but most can learn how to blow up the bigger ones. So for about 30 minutes he shown me how to do it. I can blow up the 360's and even though they are a little bigger they will work for the hood of the Bivy. They also are the same size as the CheerStics so they will replace the CheerStics in my Kilt / Air Pad Shell. When I blow up the 360's for the Air Pad I will tie them off at about 24" long. He also showed me how to tie a sort of slip knot that I can take out easy. With the stronger balloons and the slip knot I know I can use them more than once. His balloons are stronger but not heavier (3 grams each) than the ones I had been using from Hobby Lobby.

I have had a chance to use the bivy for 6 nights on my Georgia Hike. Most nights were a little windy and I kept my head inside the hood area. When I thought about it I tried to keep the hood open a little. It never got bad enough to try the balloon idea. I did get a few condensation drops one night when I was real close to a river but never enough to worry about. I think the breeze blowing through my tarp set-up most nights may have helped. The weather which was cool and dry might also have helped. I slept on the ground with just a ground cloth two nights - no pads just the soft leaves - stuff - etc.