Time-dependent dye uptake of textile substrates can be described by a new mathemat ical model that divides the dyeing process into two parts, dye adsorption and dye diffusion. Using this model, the influence of temperature (20-80°C) and NaCl concen tration (2.5-10.0 g/L) on the dye uptake of a trichrome dye combination of C.I. Direct Blue 225, C.I. Direct Violet 47, and C.I. Direct Yellow 27 on cotton is determined from sorption curves obtained by uv-vis spectroscopy. This model can demonstrate differences in temperature dependent dye uptake of the disordered inner and outer surfaces of the substrate and also displacement reactions that occur during dyeing.