Multi-walled carbon nanotubes (MWCNTs) were functionalized with oxygen-containing surface groups and subsequently incorporated in cotton and polyester fabrics by a process that mimics the traditional industrial dyeing process. The washing fastness, hydrophobicity and flame retardancy of the functional textiles were evaluated. The MWCNTs surface chemistry was modified by three different routes: (i) liquid phase oxidation with nitric acid, in order to introduce acidic oxygen-containing groups, (ii) thermal treatment of the sample oxidized in (i), in order to remove the carboxylic acid functionalities and (iii) gas phase oxidation with 5% oxygen in nitrogen to incorporate basic and neutral groups. All samples were characterized by temperature programmed desorption, pH at the point of zero charge and N-2 adsorption-desorption isotherms at -196 A degrees C. The effect of the MWCNTs acidity/basicity and of the type of substrate in the nanomaterials incorporation efficiencies and in the performance of the final textile materials was assessed. The scanning electron microscopy images and the whiteness degree values of the functional textiles before and after washing indicated that the incorporation efficiency was higher for the textiles containing the most acidic MWCNTs, especially for the polyester textiles. The immobilization of the less acidic MWCNTs in polyester imparted hydrophobic properties to the fabrics surface; in particular, the polyester samples functionalized with unmodified and O-2-oxidized MWCNTs presented an almost superhydrophobic behaviour. In the case of the cotton-based samples, a hydrophobic behaviour was not achieved. Finally, the flame-retardant properties of both substrates improved upon the MWCNTs immobilization.