What’s Cheaper, Lighter and More Breathable than an E-Bivy? My MYoG Tyvek Bivy

As I’ve noted before, becoming a light-weight hiker can be a rather expensive process (and a lengthy one if you want something from MLD). I am on a budget and a schedule, so I’ve had to be a bit creative.

After looking at a variety UL bivies to go with my Locus Gear tarp, both Jototaro (of Locus Gear fame) and Hendrik encouraged me to try making my own out of tyvek (don’t know what tyvek is? here’s a short primer). Unfortunately, I have never done well in arts and crafts, I can’t really draw or cut straight, and I haven’t made anything out of fabric since I made a pencil case in 8th grade home-ec.

But, I did some research and manned up. Part of the whole experience of hiking across the alps is trying something new, pushing my comfort zone: trusting a bivy I made with my own uncertain hands certainly qualifies as challenging my comfort zone.

Here is advice for new light-weight hikers: when in doubt, consult the Backpacking Light forums. Once I did that, things started to roll.

This excellent BL thread convinced me I was capable of making a bivy and, since I don’t have a sewing machine, to use 3M Super 77 spray-adhesive. So I picked some up at Tokyu Hands. As for Tyvek, Locus Gear’s sister shop Outdoor Material Mart sells all sorts of MYOG supplies including a tyvek not normally seen in MYOG projects in the US.

The tyvek they sell is 1446B, a UV blocking soft-type tyvek. It’s water resistant to 14.9 kpa (I don’t know the conversion, but 9.6 kpa is 1000mm hydrostatic head, which considered waterproof according to my research), soft and very lightweight at 47g per square meter.

I didn’t have a pattern, and decided to make it up as I went along (kind of my MO). First, I got some paper clips and made some mock up bivies to give me a sense of how different designs would play out.  After I had a decent idea, I drew out a tapering design top and bottom on two pieces of tyvek, leaving 10cm on each side for a nice fat seam. The plan was for something that resembled a MSR e-bivy without a side entry. I screwed up the first side, but busting out some trigonometry (cosine!!) managed to get long straight lines from my short straightedge on the back side.  Now I have some sweet marker lines on the outside of my bivy. Not quite FSTPKR’s trail flare, but it will do.

Next: Cut out the pieces, and glued the body section to the bottom with no problem at all. The seams are lined up so that stress from rolling etc will pull in line with the bond (just overlapped the edges of the top and bottom). For the corners at the foot end, I cut the corners and folded them in to get a smooth seam (think wrapping a present). Lucky, the Super 77 is pretty forgiving so I could mash it together a bit just fine. I did the same for the hood. The whole thing took 3-4 hours including thinking, correcting errors, more thinking, and letting the glue dry. I think the next one will clock in at less than 2.

I stood in the shower with the bivy, worked out perfectly, dry as a bone. I’m going to trail test the bivy this weekend, and if it works (ie doesn’t tear and does breath) and there is interest, I’ll post photos and more specific directions. If it’s a disaster, I’ll post those photos and warn everyone away from it.

Do you care how much it weighs?

Thought you did.  Less than 6oz. (5.8-ish). Yes sir.

The One Big Caveat:

For information on the effectiveness of gluing tyvek, this report is a must read. The conclusions, which proved true for me, is that a bonded tyvek seam is stronger than the fabric itself. However, the bond will delaminate very easily. So, if you bond the tyvek in a way that the pieces can be pealed away from each other, they will (think the motion of opening a book, stress coming perpendicular to the top edge of a bond).

In my current version of the bivy, the hood overlaps the chest section leaving a flap that will delaminate quit easily. In order to remedy this, I will either have to cut the flap OR sew a couple of stitches at this stress point to take the stress off the glue. I am planning on doing the ltater.

All the other seams, as long as there aren’t any flapping edges, appear to be very strong.

One thing I will do differently next time:

I made the hood far too long and the chest piece too short. I guess I thought I was big headed (har….). So I’ll probably glue on a flap to extend the non-hooded coverage up to my chin.

Conclusion:

A bonded tyvek bivy is an easy and fun DiY project. It seems like it will work well, and I’ll be super stoked to sleep in something I made myself. I’ve got a bit more tyvek so I might try to make another more shapely bivy, and if I can find a sewing machine on the cheap I will definitely be adding no-seem-um mesh and a side zipper.

Also thinking about making some tyvek chaps ala GG Spinn-chaps with the scraps…

If your thinking about buying a bivy, why not take an evening and try making your own first?

Do you make your own gear? Why or why not? Do you trust the stuff you make?

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About hamilton

Walking, Walking!
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7 Responses to What’s Cheaper, Lighter and More Breathable than an E-Bivy? My MYoG Tyvek Bivy

  1. jotaro yoshida says:

    Good job!
    This is one small step for man, one giant leap for your MYOG career!
    A jug fills drop by drop.
    Good Luck!

  2. hamilton says:

    Thanks! It’s really encouraging to have this and a couple of meth-stove projects done and feel like this is something I can do. I’m really looking forward to coming up with some creative ideas to test and share as I keep practicing.

    But now I am heading off to the post office to pick up a certain parcel from you…so tempting to head off to the park just to set it up tonight!

  3. It’s good to see an addition to the small (but growing) community of English-language bloggers about the Japanese mountains. And I’m intrigued by the home-made bivvy: might try one one of these days…. Meanwhile, I look forward to reading about your traverse of Japan via the high road. Adding you to the blogroll now.

  4. Pingback: Is Loving Lightweight Hiking/MYoG Genetic? | Traverse Japan

  5. Shed Dweller says:

    That’s a lovely DIY project. Apart from a ground sheet I’ve never made anthing from tyvek. I’ve never seen the soft lightweight stuff in the UK, although I’ve never really searched for it.

    Hope it passes the strength and breathability test. I always worry a bit when using home made gear for the first time. I tend to take a backup or have a backup plan on the first trip with new gear. Great post and keep us informed of the outcome!

  6. Maz says:

    With that high a hydrostatic head rating, I wonder about breathability. Was reading Ronald Turnbull’s book this morning, over a mug of tea before work, and he lamented that it wasn’t the Irish rain from the outside that was making him wet one trip in Ulster, but Scottish (i.e. his) sweat from the inside. With a down bag, this must be an issue. How has it been? Have to say though, all this talk of bivy’s has got me wanting one – do I go for an MLD Soul with a 70D base as I have been thinking about, or do I make my own as Mrs Maz is handy with a sewing machine…?

    • hamilton says:

      The BPL forums on Tyvek give pretty good reviews of the breathability. For now, I’m using a synthetic bag that’s a hold over from my heavy weight hiking days. Hendrik loves his tyvek bivy and (if I’m correct) uses a down bag without issue.

      I say you should grab some 3M-Super 77 and give a tyvek bivy a go yourself! After finishing this one though, I’m really considering trying to make something fancier over the winter…so many ideas so little time! Except for shed dweller who seems to be able to bust projects out like nothing!

      Does Mrs Maz hike with you? My lady friend got excited about making some tyvek chaps for me (she loves thrift), and its piqued her interest in lighthiking all the more…all part of my master plan…

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