Tyvek Bivy Sack for Camping/Hiking

A Bivy, or Bivouac Sack is a bag for your sleeping bag. In good weather, they keep your sleeping bag clean, in bad weather, they keep you dry (mostly)... Bivys are basically a waterproof shell that protects your sleeping bag. They have an added benefit of keeping dew off your sleeping bag, and slightly increasing your warmth. The only down-side is that the bag will trap moisture (perspiration) in the bag. In hot/humid conditions, this can be a big problem.

In this Instructable, I'll show you how to make a cheap bivy that works well in decent weather and is not terribly heavy. In rainy conditions, you should have additional shelter over you. (Commercial Bivys start around $80.)

This bivy is constructed from 14'-15' of 3' wide Tyvek House Wrap, and double-sided carpet tape. The basic design is a full length of tyvek folded at the foot and sealed on the sides.

One important note: This bivy does not breathe. Never seal up an unvented bivy over your head!

Step 1 Materials/Tools

Required Materials:
Approximately 15' of 3 foot-wide Dupont Tyvek Home Wrap (or similar).
Double-Sided Carpet Tape (the permanent kind)
Velcro
Tyvek Tape (optional)

Tools:
Scissors
Measuring Tape
Wallpaper seam roller (Optional)
washing machine

Build Time: Approximately 2 hours, with a break for drying the tyvek...

Comments

[mimulus3]

According to the dupont website, tyvek is water repellent (when the tyvek wording is facing out) and allows moisure/water vapor to pass to the outside from the inside. In other words, it "breathes", not las well as cotton would, but is more permeable than cling wrap or plastic. So putting this together with the words facing inside defeats the purpose.

Also, I think it is infinitely easier to cut out your pieces, wring the tyvek instead of crumpling it, then unwring, crumble into a ball and then wash. My front loading machine had no problem with this, as you do not have a "bag" yet and the water spins away.

Then you proceed as usual. I used duct tape and did not bother turning inside out to have neater seams. I am a long time fabric seamstress and it is standard practice to preshrink/pretreat your fabric before assembly. and it worked great here too.
Just hoping to add a few refinements to this great tutorial.

[ejacques]

I'm not sure but you seem to be using it with the Tyvek printing on the inside.

You should try it with the printing on the outside. Tyvek is made to "breathe" in one direction. It's basically waterproof on the printed side and the back is supposed to allow water molecules to flow through.

Great idea and since I have half a roll sitting outside and am going camping in two days, I now have a project for tomorrow!

Thanks!

[jsawyer]

Interesting. I was unsure of that, and left the printing inside for aesthetic purposes. I did a couple of google searches and there was some debate, but better to be safe than sorry...

Unless you're collecting your sweat to use a drinking water in a desert-survival situation! :-/

Let me know how it works out for you!

[ejacques]

Actually, it seems that I was wrong...

I did some research on Dupont's web site and haven't found any mention of it being able to "breathe" only in one direction. There is also no mention in the technical documentation of needing to install it with a specific side facing outwards.

Hmm, I guess we were simply told this so that the printing would be visible.

I didn't actually try it. I was going camping with someone who had never gone before and he felt more comfortable with us using a tent. But I'll definitely try it.

Thanks again!

[hpstoutharrow]

Great choice of material Seems perfect for this application! Question: Does the Tyvek lose any of its weatherproof ability when it is softened by wrinkling and washing?

[jsawyer]

I have found that repeated use does allow some leakage, but it's minor at best. The first washing doesn't break down the structure enough for it to leak. Since it won't absorb water, the vast majority of it rolls off anyway. Even if you HAD a leak, it would take some water pressure to actually go through the fabric... So I guess that means don't use it to make waders, or a boat... Unless you use lots of duct tape to seal the seams. :-)

Though tyvek is "breathable" having such a small area tends to collect moisture.

The size I made is really kid-friendly, I'd need another piece put in for it to be roomy enough for me. I fit, but it's a bit confining.

[jsawyer]

From everything that I've read, unless you wear a hole in it, it stays waterproof... You have to be careful when removing it from the washer, as the bag will hold water! At some point, the tyvek will peel a part before the tape will fail. One thing I've found with this bivy: It's a perfect size for a smaller person, but I'm a bit too big, I don't have the room I need to comfortably roll over (I flop a lot in my sleep). I might just build a larger version, and taper it to fit my mummy bag. I made smaller bivys for my kids, and they work really well. Just for fun, I crawled into the bivy with my Therm-a-rest and a blanket. After a couple of hours, I could feel the moisture building up, but as I understand it, this is not unique to tyvek.

[TrailH4x]

Nice! I've got a small sheet I have used as a ground cloth under a tarp, but never thought of builidng a bivy out of it! Great concept!

[DELETED_GuardianFox]

(removed by author or community request)

[jsawyer]

Thanks. I've heard heat-welding is not great as you lose the benefits of the random fibers and the material weakens. I just bought some weldwood contact adhesive... it's supposed to work pretty well for low-loads... might work. I'll try sewing it sometime, but the double sided tape is just too quick and easy. I have a tyvek tarp, I'm thinking about building a caternary cut tarp out of tyvek... on the main seam, sewing might be a better idea than a wide taped seam. Thanks!