Recent advances in experimental methodology now permit the quantitative kinetic study of the mechanisms by which fabrics such as cotton take up dyestuffs. This article first describes results obtained from the dyeing of cotton and nylon cloth using the azo dyes Orange G and Sunset Yellow FCF where the uptake of dye by the fabric depends essentially on the physical solubility of the dye in the substrate. The mechanism of dyeing of these dyes is then compared to reactive dyes based on dichlorotriazinyl species. With these dye a covalent bond is formed with the fabric. The channel flow cell studies show that both types of dyes have a common mechanism for the uptake of dye through the solution. Dye must diffuse through a porous surface layer to reach the bulk cloth. The passage through the surface layer becomes restricted by dye adsorbing onto surface sites in the porous layer which can be approximately described by the Langmuir isotherm. The uptake of dye into the bulk cloth then follows a first order reaction mechanism.