Here's a pretty straightforward tip on using RIT dye
Pretty much says to AVOID trying it on synthetics and fabrics made with waterproofing layers to it:
Here's What Rit Will & Will Not Dye
Choose Your Fabric & Materials
Rit works best on many natural, washable fabrics and materials, such as ...
- 100% cotton, linen, silk, wool, ramie
- Synthetics such as rayon and nylon
- Fiber blends with at least 60% cotton or other dyeable fiber
(Blends will tint evenly but will not achieve full color)
- Nylon-based plastic such as those found in buttons, fasteners, golf balls & lacrosse sticks
- Natural materials such as wood, wicker, paper, feathers and cork
... but there are fabrics and materials that will NOT accept dye such as ...
- 100% polyester, acrylic, acetate, fiberglass, spandex and metallic fibers
- Fabrics with rubber backing (bath mats or throw rugs)
- Fabrics with special finishes such as water repellents
- Fabrics with bleach damage or extensive staining
- Fabrics washable only in cold water or labeled "dry clean only"
- Polyethylene plastics such as golf discs
- Polycarbonate plastics such as eyeglass frames
If you are in doubt as to whether your fabric will accept dye, test a swatch.