Abstract: An injection moulding apparatus (10) includes similar co-injection modules (12) each provided with common supplies (238-242) and supplied with different polymer materials at intermediate pressure by common plasticisers (14-18). Each module has a co-injection nozzle assembly (70) in wich each nozzle (148-154) is supplied with polymer at injection pressure by an injector (208) which receives polymer through a non-return valve (220). The injector is mounted alongside the nozzle on a polymer transfer plate (138-146), and has the position of its piston (212) controlled by a hydraulic actuator (214) under the control of a dedicated micro-processor (164) in accordance with a stored injection control program. Each polymer is injected by an injector (208) directly into the associated nozzle (148-154) and is controlled solely by injector operation, and without the use of any control valve between the injector and the nozzle.