DWR (durable water repellent) is a coating added to fabrics at the factory to make them water-resistant (or hydrophobic). Durable water repellents are commonly used in conjunction with waterproof breathable fabrics such as Gore-Tex to prevent the outer layer of fabric from becoming saturated with water. This saturation, called 'wetting out,' can reduce the garment's breathability (moisture transport through the breathable membrane) and let water through. As the DWR wears off over time, re-treatment is recommended when necessary.
A DWR can be reapplied (perpetually, in fact) via a spray-on from companies such as Dry Guy Waterproofing.
