Hi John-

I've had great luck with Nikwax with all kinds of fabrics. Took a while to figure out which treatments were ideal for different fabrics, but their website explains things pretty well.
http://nikwax.com
Did not notice a change in the fabric at all. I've used it on breathable stuff (gore-tex, hypertex, etc), leather boots, down sleeping bags, and fleece.

There's also the Granger's brand of treatments. Same kind of thing, though I've heard their recipe is a little harder on the environment, but haven't verified that claim.
http://www.grangersusa.com

Good luck,
Jason