I've spray paint stenciled clothes for a while, and have a few shirts that I spray painted about 7 years ago that still hold strong. After a good hanging out to get the fumes out and a run through a washer, it's all ready to wear.
I'm planning on doing some more thorough experiments and will share notes as I go.
Step 1: Make a Stencil...
The trick is to go very light with the first spray you do. If you spray a thin even coat on your paper, and let it dry, then repeat, ie, build up slowly, you get a waterproof coating on your stencil paper. If you spray too hard you can soak or sog it down and it either gunks up or rips and falls apart.
I made some stencils on a whim after pulling a cardboard donut out of a 2gal glass bottle I bought and thinking it would be a nice frame for a stencil.
The other bits are just duct tape and printer paper cut after being folder over 2wice and cut out with scissors (I reinforced their bottom with ducttape).
Step 2: Weigh Down and Spray...
As long as you spray over your stencil in a gesture that's like petting it down with your hand you can keep nice sharp detail. Don't rush to force out a super dark spray the first time. You can hit it light, let it set, and spray onto that. Repeat as you need. I like one light hit on the fabric so it's softer looking and doesn't have too much junk hanging out on me.
Step 3: Check 'em Out!
I know this was a quick and dirty instructable, but maybe its useful to someone to get some ideas rolling?
Have fun, share cool stuff!
Step 4: More Stuff
tree cut out I did a few years back. I lost the stencil, I liked it.