Beer＇s law of light absorption and the Kubelka-Munk analysis are applied to absorbing-scattering fabric ic. A relation between the Kubelka-Munk function F(R) and the absorbance of dyed fibers is proposed. The relation is used to predict the absorbance of a colorant from the reflectance of a substrate dyed with it. Samples of polyester fibers dyed with different colorants are used. The predicted absorbances of these samples agree fairly well with those measured directly on the spectrophotometer.