I use spectra or spiderwire fishing line, which (since intended for outside use) is more UV stable. I've been able to sew with them, and have used the 30# test line to lash a shelter. Some knot choices don't work well on this line, but the spools usually come with instructions about this.

I took Doug's PSK pencil, put it in a drill motor, tacked the first row of Spiderwire with hot glue, and cranker 'er up! You can wind many yards of this line on that pencil and not increase the bulk that much. Then I finish the spool with a tiny strip of electrician's tape to keep it from unspooling.

I've never used kevlar thread, but can't imagine what it would give me that the Spiderwire won't.