Substantive dye is a dye

Dye

A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....

 used in a process in which dye molecules are attracted by physical forces at the molecular level to the textile

Textile

A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

. The amount of this attraction is known as "substantivity": the higher the substantivity the greater the attraction of the dye for the fiber

Fiber

Fiber is a class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread.They are very important in the biology of both plants and animals, for holding tissues together....

. Substansive dyes work best on textiles with high contents of fibrous cellulose and are set in a slightly basic or neutral environment at high temperatures close to boiling point. Substansive dyes are set by hydrogen bonding.