Nikwax Polar Proof is a wash-in waterproofing for fleece, wool, fiber-pile and synthetic fabrics. This product helps to maintain the air gap between the knit and the weave of your apparel, thereby trapping more air to keep you warm. Nikwax Polar Proof renews the water repellancy and breathability of the garment. By washing your clothes with this you are also prolonging the life and performance of your gear. Note from Nikwax: Remember to clean gear first with Nikwax Tech Wash before applying Nikwax Polar Proof.