My hubby wants to make his own bivvy sack. Any ideas, designs online or your designs, etc? Anyone make one? He wants to make it out of sil nylon. Thanks!

I made one from the Quest Outfitters pattern. Not enough netting, poor face room, and awkward to use: but a good learning experience. Their web site has a couple pictures.

Subsequently bought a Solanthe. It's nice. But it's not a tent, too small for that. Hard to get much if any gear inside. I like it best for cool to cold weather, with no more than light rain, since I often get up in the night and that's wet.

Recommend getting one used, trying it for a while, and seeing what you like or don't like before making one.

Blissful, if he plans use this as a stand-alone shelter, I would suggest something like this design: http://www.backpacking.net/makegear/dj-tent/index.html. Sil-nylon does not breathe so ventilation is imperative.

If he is considering a true bivy sack, he needs to make the top from something like gortex, tyvek, ect. that is both waterproof and breathable.

The basic pattern is pretty straightforward -- it's just a coffin-shaped bag made of silnylon on the bottom and some breathable fabric on top. (No silnylon on top -- the condensation inside will soak his bag.) Remember to make it wide enough ('girthy') so he can put his sleeping pad, sleeping bag, and himself inside.

The traditional bivy sack has a slit opening across the chest, usually with a zipper, sometimes with a small piece of mesh. This sucks. It's very difficult to get in and out of a bivy like this, in my experience. I like a bivy with a side zipper, one that goes around the outside of the bag from one shoulder to the other hip (and matches with the sleeping bag zipper). This makes it much easier to get in and out of the bivy under a small tarp or wherever. I also like about 1/3 of the top fabric to be noseeum mesh, for breathability.

Here's a photo of my old Mountain Hardwear bivy with these features:

http://tinyurl.com/2crcgb

Just ignore the ugly hiker in this photo. You can also get ideas from some on-line bivy makers:

http://tinyurl.com/94arz
http://tinyurl.com/2gqmew
http://www.titaniumgoat.com/Bivy.html

Hope this helps. I'm doing the same project this month, and I'll try to post some photos when it's done.

http://www.backpacking.net/makegear/tarptent/index.html
Or just go with the original. If he wants to use silnylon then he is making a tarptent-type structure. A bivy needs to be waterproof breathable and silnylon is simply waterproof. If he is realy into doing it himself then making a shaped tarp is not that hard. The basic technique is to use a polyethelene tarp and duct tape to make a pattern then use silnylon to make the final product.
OR...
http://www.questoutfitters.com/patterns-tent,sleeping%20bag.htm#BILGY%20TARP%20TENT
OR...
http://www.sixmoondesigns.com/ultralight/myo_Meteor.asp combined with a small tarp
TB

there's this:
http://www.sportsmansguide.com/cb/cb.asp?a=271436&kwtid=200242

but i think rubberized cotton would be rather heavy? i guess the plus side is that it's cheap so you can buy it just to test what using a bivy would be like..