I guess you would need ultraviolet protection for it. That's the primary cause of fading in something exposed to the sun. My one nephew does some climbing and he used this stuff called Granger's UV Spray On Waterproofing. I can't tell you what kind of fabrics he sprayed it on though. He said it was for restoring spent waterproofing on water repellant clothes he had, and it was a UV protector as well.
I did a search and found their site. Maybe you can find some answers there.

Here is a link that might be useful: Granger's Waterproofing Products

I bought a UV Block online last year to use on my porch tablecloth and chair cushions. It did a good job of preventing fading. Their web address says it's www.atsko.com

THANK YOU! Great information, I am looking thru it all now! Karen

try your local fabric store, they should have some there. I think it is 3M product?

Krylon makes a UV Fabric Protector in a spray can. You can buy it at Walmart.

Hi all,
Just was Googling re: Sun/UV protection spray and found this page, but some of the links on here are no longer live.
My specific question is, I just bought some silk fabric for bedroom curtains, but being in Arizona, I am worried about the sun fading the fabric.
What I'm reading about the UV sprays here is they seem more geared to use on heavier fabrics, like canvas, to improve their longevity. What I need is a spray that first of all, won't create spots on my silk fabric, and is generally safe for use on silk (won't eat the fabric,etc), and of course, will help keep the color intact.
I do understand that silk in general won't hold up in the sun as long as say, canvas, but these are indoor curtains.
Any advice?

For the silk I would use a liner for drapes

Absolutely. Line them, that's the best bet.