No suitable method for the coloration of unmodified polypropylene using aqueous dye solution has yet been found. Currently, the only viable method is the incorporation of pigments during the extrusion of filaments. In this study, two different commercially available forms of pigment (powder and masterbatch) were incorporated into polypropylene before extruding into filaments to examine their effects on the mechanical behaviour of the filaments. It was found that increasing the pigment content generally reduces tensile strength and Young's modulus in both masterbatch-pigmented filaments and powder-pigmented filaments. However, the extent of reduction is also markedly dependent on the type of pigment incorporated. In addition, elongation to peak is much higher for masterbatch-pigmented filaments than for powder-pigmented filaments. © 2006 The Authors. Journal compilation © 2006 Society of Dyers and Colourists.