This stuff was developed in England where they know a thing or two about liquid sunshine.

Here is what they have to say.

Nikwax manufactures high quality cleaning and waterproofing products.
Nikwax prolongs the life and enhances the performance of clothing, footwear & equipment.
Whether you work or spend your leisure time outside, Nikwax keeps you dry.

Nikwax products are EASY to use. The products go exactly where needed; less product is wasted, saving you money. You can treat gear with Nikwax in your washing machine, by hand or by using our spray-on products.

Nikwax products are SAFE to use. No propellant gases, non-toxic, no fluorocarbons, environmentally safe. It’s WaterBased. By using Nikwax you can renew your gear and reduce the impact on the earth's resources.

Nikwax products keep you DRY. Nikwax ensures you get maximum performance from your gear so you stay dry, warm and comfortable in wet weather. Enjoy your time in the outdoors (even if it is work!!)

Stay dry, warm and comfortable with Nikwax Waterproofing.

The principle of using Nikwax is:

Green for clean
Purple for proofing

More info at their UK site