A substantive dye is a type of dye that bonds strongly to the fiber it is applied to, resulting in long-lasting color that doesn't easily wash out. There are several synonyms for substantive dye, including reactive dyes, direct dyes, and fiber-reactive dyes. These dyes are commonly used in textile industries to color natural and synthetic fibers such as cotton, silk, and polyester. Substantive dyes are also preferred by many consumers because they are eco-friendly and don't contain harmful chemicals that can harm the environment. Additionally, the dyeing process using substantive dyes is easy and can be done at home without the need for industrial equipment.