2d bivvy sack pros/cons

[Joseph Williams]

Hey folks, I'm designing a bivvy sack for a my tarp/bivvy quilt system.

I'm wondering if I can get away with a 2d design without boxed walls for the sake on simplicity.

materials are silnylon for the floor and momentum for the upper.

has anyone had success/spectacular failure with such a bivvy sack?

[Peter McDonough]

Cut the top a few inches shorter all the way around and sew like a stuff sack. It works…and it gives you a bathtup floor all the way around. I had great success with this design.

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=2771

[Ernie Elkins]

As I understand it, this is how Ti Goat makes their bivy sacks. They sew them flat and rely on your sleeping bag loft to lift the seams off the ground. I know that there are a lot of satisfied Ti Goat bivy owners out there, so it must work effectively enough.

[David Wills]

i've made VB liners with both 2D and stuff sack style bottoms. the stuff sack style bottoms are far superior in my opinion. Just more comfort for feet and more efficient use of materials.

[Jan Rezac]

There are both pros and cons for the 2D design:
+ simple construction
+ waterproof bottom – no seams in the wp. fabrics
+ multi-purpose: nice large groundsheet
– extra material in corners = extra weight
– 3D design couples better with sleeping pad

The decision is up to you, I'd chosen the 3D pattern when I was making mine, because I wanted enough room for my winter bag and the weight saving was worth the extra work for me.

[Joseph Williams]

Thanks for the reference to the Ti Goat bivvy…I can see the arguments for 3d (thanks for the examples, folks!), but I suspect that for my dwinlding sanity, I shall end up doing it in a titanium goat stylee!

Crazy Pete: Nice tarp!

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