MYOG: tyvek ground cover / bivy combo

[t.darrah]

Here are a few pictures of my second GCB model. The first now known as GCB-1 is a classic slide in style ground cover bivy. GCB-2 has a roll down top section in the top cover.

This GCB-2 with the roll down top will allow for easier access into the ground cover bivy. This will be useful if used inside a single wall shelter where room is limited. The roll top overlap provides required coverage/protection if used without shelter.

[Casey Bowden]

Thom,

Your new bivy looks good. FYI, to make your photos line up vertically rather than horizontally just add add rows (by hitting enter) between your photos.

[Chris Chastain]

I used a tyvek ground cover with my tarp last year on a 5 day thru hike of the Foothills Trail, during which it rained for 3 days/night straight. One night there was severe thunderstorms moving through my area.

I glued a foot pocket at the foot of the cloth using another piece of tyvek and super glue. I figured it would help to keep my bag in place during the night.

The super glue (cheapy dollar store brand) worked very well.
The bottom is folded along the line you can see, and the little tabs were just folded over the little half oval shape, and glued a couple at a time. Made sure that the pocket was just narrow enough to "bathtub" the end of the tyvek a little and tall enough not to compress the down. This pocket is too small for my winter bag, but worked great on my 14oz top bag.

In practice, it allowed me to keep my head well in from the edge of the tarp, and not worry that my feet were poking at the other end. Not only did it protect the foot of my down bag from blowing rain, but the tyvek also withstood the 1/4 – 1/2" deep puddle that I slept in during hardest periods of rain.

After the thunder died down and I got some sleep, I awoke to a dry bag. There was quite a bit of sand that splashed up on it from the puddle, but the DWR finish handled that fine. This thing worked well and weighs about 4.5oz.

It is my opinion however that tyvek won't breath well enough for a complete bivy. I hope I'm wrong.

[Eric Blankenship]

Hey Thom-

I am curious how the testing of your Tyvek bivies is coming along. Any updates?

[David Erekson]

Looks good for a bivy.
As for some of the questions on Tyvek, here is what Dupont says. I am paraphrasing from the Dupont website. Basically, there are three types (10, 14, and 16). Type 10 is hard structure, and 14 and 16 are both soft structure. The soft structure is what is used in garments. The hard structure is what homewrap is made of. Only type 16 has little pin holes. Tyvek is not waterproof, but does have a hydrostatic head. There are 8 types of hard structure. 6 of the 8 type of hard structure have a hydrostatic head of <15 in. of H2O. For the other two, their hydro head is 59 and 62 in. of H2O. These two are used in Medical packaging (so I am guessing that homewrap has a hydro head of <15). They don't have numbers for the soft structure hydro head (probably because it ain't that great). Anyways, the more water proof, the less breathable. So, by mixing a highly waterproof tyvek with one that breathes more, would make a good bivy.

[t.darrah]

I will be posting an update soon, thanks for the continued interest in my project.

[G Dup]

Had a few questions…

How does the tyvek handle water running under it or say laying in a puddle? I have used some lightweight tyvek before and I found that it wasn't terribly waterproof. Is this housewrap better? What about the plain white variety?

I'd imagine the crinkling could get old fast. You can put it in the wash a few times to remove this, right? Does that seem to affect waterproofing?

What about sealing the seam, has this been mentioned?

Have you had any tearouts, particularly on the topside of the bivy on the edges near your shoulders?

[t.darrah]

G Dup,
I will be providing a project update soon, including numerous trip pictures. But below is my attempt to answer your questions regarding tyvek.

1) Tyvek is not waterproof but highly water resistant. Perform this simple test at home; secure a piece of tyvek (use large rubber band…) over a large bowel or small bucket and form a concave depression in the fabric, fill the depression with water and let sit for a couple days: water will not penetrate the tyvek, the interior of the bowel or bucket will remain dry. In my testing I have never had water penetrate through the tyvek material from above (rain) or below (wet ground). As with all water proof or water resistant materials/fabrics interior moisture in varying amounts can occur as the result of condensation. I would be happy to send any BPL member a small piece of tyvek to perform this test at home, PM me if interested.
2) Tyvek will soften with use and/or washing, this has not effected the water resistant quality of the material in my experience and testing.
3) I have been using bonding in place of sewing which eliminates the need to seal seams. Sewing would allow for a smaller seam allowance (IMHO), but sewing would require seam sealing. I'm searching for a good quality used sewing machine now so that I can experiment with both methods, sewing and bonding.
4)I have experienced some material tearing during testing but I believe this to be more the result of design and fabrication then material performance. Tyvek is very tough and durable for such an application. My MYOG design is continuing to evolve and my fabrication/workmanship improves with each attempt so this will hopefully become a non issue.

Feel free to PM me with any additional questions.

[Richard Allen]

Thom, I am very interested in purchasing a Tyvek bivy from you. Would it be OK for you to give us some details here or do you need to discuss these matters in private? If the latter you're welcome to PM me and we can exchange full contact info.

Peace,

Richard.

[Charles Mason]

I read somewhere way back that Tyvek works by letting buildings breathe somewhat by design which is why it's not waterproof but just resistant. This means if the large blue prints are on the inside, it will virtually stop the breathability of the building and reduce the water-resistance capability, ie: the worst of both worlds.

[t.darrah]

Charles,
I've fabricated tyvek GCBs for personal testing using the fabric both ways and have seen little if any difference in performance, but this may be due to test conditions where used. When making GCBs for others I always use the wording side of the fabric as the outside facing surface.

[David Erekson]

Charles, it doesn't matter which way the tyvek is facing. It breathes because it's pores are smaller than liquid water, and larger than vapor. There isn't a waterproof side and a breathable side, it is one continuous fabric with the same properties on both sides. Hope that helps.

[Charles Mason]

DuPont FAQ:
Can DuPont™ Tyvek® be used with the lettering facing in?

DuPont™ Tyvek® HomeWrap®, DuPont™ Tyvek® StuccoWrap®, DuPont™ Tyvek® DrainWrap™ and DuPont™ Tyvek® CommercialWrap® are equally effective in both directions. However, DuPont™ Tyvek® StuccoWrap® and DuPont™ Tyvek® DrainWrap™ have a specially engineered surface that should be placed with the grooves in a vertical direction.

[Michael Barber]

Perhaps we have all been duped and misled by the ebay tyvek sellers who sell tyvek with logos and needed an advantage over the guys selling plain white. I know that is where I heard the whole thing about tyvek needing to be used in certain directions.

Thanks for clearing that up. I'd like to not be a hiking ad for Dupont!

[Eric Fitz]

Hi guys. I just registered after reading though this thread so I could give you some tips on working with Tyvek.

I create all sorts of things with Tyvek and use an "Impulse Sealer" to bond it to its self.

You can't get a better deal than this one:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=43477

The advantage to doing this is there is no glue and no holes. it basically just melts together.

You can use this same approach for what you are doing. Since you probably want curves and stuff try using a continuous heat roller sealer like this:

http://pacnseal.com/roller_sealers_constant_heat.html

(several places sell them so google the prices)

That's going to be a little trickier than using an impulse sealer with a timer on it because you will have to figure out how fast you need to move along your line to bond, but not melt so much you cut.

This should give you some ideas for cranking these things out fast with little mess.

If you go into full on production there are a few places that will float dye the tyvek to pretty much any color, but you have to buy some large rolls. These guys will do it:

http://www.materialconcepts.com/index.asp

Good luck!

[t.darrah]

Eric, I will look into each of these suggestions. Thanks for taking the time to post your ideas/comments.

[Stephen Lastname]

Has anyone ever flame tested that stuff. Like if you were cooking in the bivy and knock your alcohol stove over – would you be entombed in a melted cocoon of tyvek? I ask this because I remember a post on another board of a guy who made a tyvek tent for his kids and had them in there with candles and someone quoted the flame retardent specs and warned against open flame. I have a dwr top/tyvek bottom and love it. I rolled the tyvek up on the foot end about 12" to form an overkill bathtub and give better protection on that end since I sometimes slide toward that way. My feet seem to breath very well and the tyvek keeps the rain out. Works great. I had no problems sewing the dwr to the tyvek, but did not seal the seams.

[Eric Fitz]

If you want/need fire retardant tyvek you want 2075D.

There might be some sprays you can use to coat normal tyvek. This might be a better approach since normal wear will probably cause the 2075D to be less effective. You can just respray.

Tyvek burns. Try it on a scrap so you know how it behaves.

[Doug Johnson]

I am wondering if there has been any progress on this project…this idea has some teeth, let's keep it going!

[t.darrah]

Doug,
I will be posting an update soon with trip pictures of the GCB in use.
Thom

[Brett Peugh]

So what ever happened with this?

[Keith Selbo]

Yeah, what ever happened?

[t.darrah]

I'm still very much working on this project. I've redesigned the cut so that I now have only one seam instead of two and I've incorporated a foot end vent (which I'm still refining). I found the tyvek bivy to warm for summer use but it has worked well this fall. I'm hoping the foot end vent will help by letting out some built up heat and increase air circulation. I have experienced no noticeable condensation, on occasions the interior face of the tyvek would feel damp, or moist, but have no noticeable moisture and my sleeping bag would be dry. I will try to post some new pictures of the redesigned cut and the foot end vent soon.
I've enjoyed seeing TT and others make use of this material with good results and reviews.

[Ralph McNall]

Have you had it out in any rain or heavy moisture like fog, and do you use it under a tarp or out in the open? Last weekend I started on a driducks bivy, but it was a toss up between that and tyvek …

[JJ Mathes]

Hi Thom- I was thinking about making a tyvek bivy for a one night trip. I've never used a bivy or tarp, my upcoming trip will be my first with both. I have the tarp, but no access to a bivy, don't want to spend the $$$ for one until I know if I'll like sleeping under a tarp.

Anyway I did a search and found your thread, after reading the posts I'm wondering if you've made a decision on the best adhesive

ALSO, will someone be kind enough to tell me how to PM Thom. I'm sure I have overlooked something in the process of trying.

many thanks
JJ

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