This paper outlines the application of factorial experimental design to the processing of polypropylene (PP) fibres. Two examples are given. The first covers the effect of meltextrusion conditions on the overall orientation of the PP macromolecular chains in as-spun fibres. The second covers the effect of drawing conditions on crystallographic order and chain orientation in the first-stage drawing of as-spun PP fibres. © 2001 Kluwer Academic Publishers.