A method of manufacturing an object, the method comprising: feeding a filament to an extrusion head, the filament comprising a semi-crystalline polymeric reinforcement portion and a polymeric matrix portion which both run continuously along a length of the filament, wherein the reinforcement portion has a higher melting point and a higher crystallinity than the matrix portion; raising the temperature of the filament in the extrusion head above the melting point of the matrix portion but below the melting point of the reinforcement portion so that the matrix portion of the filament melts within the extrusion head, thereby forming a partially molten filament within the extrusion head; extruding the partially molten filament from the extrusion head onto a substrate, the reinforcement portion of the partially molten filament remaining in a semi-crystalline state as it is extruded from the extrusion head; and causing relative movement between the extrusion head and the substrate as the partially molten filament is extruded onto the substrate in order to form an extruded line on the substrate, wherein the matrix portion of the extruded line solidifies after the extruded line has been deposited on the substrate, further comprising temporarily raising the temperature of the filament in the extrusion head above the melting point of the reinforcement portion after the extruded line has been formed on the substrate, thereby forming a break in the continuous reinforcement portion and an end of the extruded line formed on the substrate, then lowering the temperature of the filament in the extrusion head below the melting point of the reinforcement portion to enable a further extruded line to be deposited on the substrate. feeding a filament to an extrusion head, the filament comprising a semi-crystalline polymeric reinforcement portion and a polymeric matrix portion which both run continuously along a length of the filament, wherein the reinforcement portion has a higher melting point and a higher crystallinity than the matrix portion; raising the temperature of the filament in the extrusion head above the melting point of the matrix portion but below the melting point of the reinforcement portion so that the matrix portion of the filament melts within the extrusion head, thereby forming a partially molten filament within the extrusion head; extruding the partially molten filament from the extrusion head onto a substrate, the reinforcement portion of the partially molten filament remaining in a semi-crystalline state as it is extruded from the extrusion head; and causing relative movement between the extrusion head and the substrate as the partially molten filament is extruded onto the substrate in order to form an extruded line on the substrate, wherein the matrix portion of the extruded line solidifies after the extruded line has been deposited on the substrate, further comprising temporarily raising the temperature of the filament in the extrusion head above the melting point of the reinforcement portion after the extruded line has been formed on the substrate, thereby forming a break in the continuous reinforcement portion and an end of the extruded line formed on the substrate, then lowering the temperature of the filament in the extrusion head below the melting point of the reinforcement portion to enable a further extruded line to be deposited on the substrate.