Cotton proof works by coating the individual fibres with a flexible water repellant treatment so they cant soak up as much water whilst allowing moisture vapour to pass through. This process reduces weight gain from water ingress & maintains the natural breathability of cotton. Easily applied in a washing machine, which ensures the treatment gets right thorough the fabric. However if garment care instructions restrict machine use, hand proofing is effective. The Durable Water Repellency (DWR) develops on air drying, there is no need for tumble drying. For used & dirty clothing we we recommend that the garment is first cleaned with Nikwax Tech Wash on a separate cycle, there is no need to dry before re-proofing, just bung in the Cotton Proof & start another wash cycle. Nikwax waterproofing products are completely environmentally friendly. They are water based, non aerosol, non -flammable, non hazardous, contain no harmful solvents or volatile organic compounds & are completely free of flurocarbons. Which is nice. Adds water repellency Maintains breathability Prolongs life & performance Can be used on wet fabric No need to tumble dry to activate product Inhibits mold & mildew growth Completely environmentally friendly Flurocarbon free