In this study, modification effects of cellulose foil by cellulase enzyme are studied in respect to topography changes by means of atomic force microscopy (AFM). The results provide useful information to understand the enzyme action in the amorphous and crystalline regions of cellulose. It was revealed, that the treatment of cellulose with the cellulase enzyme depends on its concentration, which selectively attacks amorphous cellulose regions. At lower concentration, a random surface roughening of the cellulose foil was observed. With increasing enzyme concentration, the cellulose surface became smoother. On the basis of this knowledge, a conceptual model to describe the conditioning effect by cellulase on the cleanability of cotton fabrics was developed. With the help of this model, we are able to estimate changes in the nanoporosity of cotton fibres.