Fiber-reactive dyes molecularly bond with fabric, creating colorfast and long-lasting shades. They’re used on cellulosic fabrics such as cotton, linen, hemp, rayon and Tencel, and can also be used with wool. Most fiber-reactive shades are classified as low-impact because they meet the requirements of the Oeko-Tex Standard 100, an international textile certification program. To meet this standard, low-impact dyes cannot contain toxic substances, must have an absorption rate in which 70% or more of the dye is absorbed by the fabric and require relatively little rinse water.