Durable Water Repellent (DWR) is a hydrophobic
chemical treatment applied to the face fabric of garments, tents, and gear to
make them water-resistant. It causes water to bead up and roll off, rather than
soak into the fabric.

Far from being a standalone waterproof solution, DWR works in partnership with
waterproof membranes (like Gore-Tex) to maintain breathability and prevent
"wetting out" — when a fabric saturates and hampers moisture escape from within.