Water repellent refers to a material or coating that is not easily penetrated by water, especially as a result of being treated for such a purpose with a surface coating. Water repellent materials are designed to resist water penetration but are not completely waterproof. Instead, they are designed to keep water from saturating the surface, causing the material to bead up and roll off, which makes water-repellent materials ideal for outdoor gear and clothing that require waterproofing while allowing for breathability. Water repellent coatings are commonly added to fabrics at the factory to make them water-resistant (hydrophobic). Most factory-applied treatments are fluoropolymer based; these applications are quite thin and not always effective. 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. As the DWR wears off over time, re-treatment is recommended when necessary. Many spray-on and wash-in products for treatment of non-waterproof garments and re-treatment of proofed garments losing their water-repellency are available.