Why do reactive dyes have excellent colorfastness?

Reactive dyes possess excellent colorfastness because they form a covalent bond directly with the fiber during the dyeing process.123

Unlike other dyes that rely on weaker physical interactions—such as adsorption, ionic forces, or hydrogen bonding—reactive dyes undergo a chemical reaction that anchors the dye molecule to the fiber. By becoming a permanent part of the fiber's molecular structure, the dyestuff is significantly more resistant to being removed by washing or exposure to moisture compared to dyes that merely adhere to the surface. This chemical linkage ensures a high level of wet fastness, making them particularly effective for materials like cotton.243