Fiber reactive dyes are textile dyes that form a covalent bond with the fibers of the textile. This results in a long lasting, bright dye that will not fade. Its a more expensive and challenging process than conventional fabric dyes, but makes the colors fade-proof.
The earliest fiber reactive dyes were designed to interact with cellulose fibers, such as bamboo, linen, and hemp. The dye interacts with the cellulose molecules, forming a permanent bond. After the linens are rinsed and dried, the dye sets, and it will never come out.