In anticipation of having a working sewing machine again, i've been reviewing my queue of projects. I have been planning on sewing a silnylon tipi to replace my disintegrating silnylon Kifaru knockoff, and had actually started the prototype, but the sag on the tent after a night of condensation is unbelievable. i seem to recall that coated nylon doesn't have the sagging problem.
is a 1.9 oz pu-coated ripstop the lightest i can get while avoiding the sag?
The issue isn't really the sil, but the nylon portion of the equation. Try using a polyester fabric instead. Poly doesn't stretch as much as nylon does when exposed to wet/cold, hence greatly reduced sag.
The good news is there is a lighter than silnylon fabric out there that is poly, the ever popular Spinntex (used by MLD and sold by thru-hiker.com). It's a spinnaker fabric that was somewhat redesigned to work well for outdoor gear. It's .97 oz/yd2 with coating, so could save you a few ounces over the course of the project.
The bad news is, there is currently a shortage and it isn't available right now. You may be able to find some standard 1.9oz ripstop with a PU coating in poly, so check around at some of the usual sources. Folks over on hammockforums also report finding some in the bargain bin at WallyWorld.
Loc: Central Texas
All coated nylon sags, and PU coated fabric sags worse than silnylon in my experience. BK is right about polyester. The lightest currently available waterproof fabric is Cuben, variously 3 or 4 oz. I like Spinniker better, but as he notes, it is hard to find right now. The Rainshed has it for $17/yard.
spinnaker is also really loud and really expensive. i'm looking at a very large quantity of fabric for this project. i didn't realize that all nylons sag. i may have to see if I can reduce the sag by catenary means, which I'm not at all comfortable with. curses! thanks for the input.