1. A method suitable for optimizing parameters which are characteristic of a preselected portion of an object comprising composites of different homogenous materials developed in a material extrusion system, which method comprises the steps of: (1) identifying an object characteristic space comprising at least one dimension, the or each dimension defining a continuum represented by gradations of a single measurable property for one object parameter; and (2) selecting a predetermined subset of said object characteristic space comprising desired optimal characteristics of the preselected portion of the object; so that when an object is fabricated by extrusion, it comprises the desired optimal characteristics.