Properties of keratin fibres, such as felting, adsorption, wetting, soiling and soil removal, are most often explained by peculiarities of the fibre surface. However, the question is usually not clarified what is precisely understood by "peculiarities of keratin fibre surface", i.e. whether specific scaly appearance of the surface is concerned, or the size of its area. According to literature, specific surface area of fibre is usually expressed through fibre geometry, or, to be more precise, as outer surface of the fibre unit mass, which in practice means the outer surface of ideal (smooth and structurally homogenous) fibre. As keratin fibres do not have smooth surface and are not structurally homogenous, we can assume that the real specific area of the fibres differs from the geometrical one. To determine the real (total) specific area of keratin fibres we have used, besides a mathematical-analytical (theoretical) method, a physical-chemical (experimental one - iodine adsorption). The investigation is aimed at determining how fineness and appearance of individual fibre scales affect on the size of specific surface area, as well as at finding out whether there exists (and what is its nature) of the impact of fibre medullation upon the value described.