I'm going to put this on a flat color and make a latex-looking fabric. I'm really not obsessed with purple. :) This is the single fold shadow brush in black.
I put the single fold highlight brush (in white) right on top of it on the same layer.
Yes, it's ugly. We're about to change that. I used Scale (Edit- Transform- Scale) to stretch it out and flatten it.
Next I set it to overlay.
Looking better already! Now to make it look like an actual fold. I used the Arc option in Warp (Edit- Transform- Warp) and pulled it down to where I wanted it.
And then rotated it to where I wanted it.
Cool, it's actually looking like a sharp, tight wrinkle. Now to add some more. I used scale and rotate on all of these to vary them.
I want my latex to be shinier! I duplicated each wrinkle layer, set it to color dodge, and lowered the opacity until it looked right.
Maybe I don't want latex. Maybe I want spandex. I'll give the whole thing a gaussian blur at 1 pixel.
Or maybe I want to make this a bolt of nice flowy silk. I'll give it a gaussian blur of 3 or 4.
Again, the brushes can be found here. Go play!