Abstract: A process and apparatus are provided for injecting dry lightweight particulate material into a stream of catalyzed resin. The dry lightweight particulate material is stored in a fluidizing tank. The fluidized dry particles are conveyed from the tank under a controlled vacuum created by a low pressure venturi pump. An anti-static conveying tube delivers the dry lightweight particulate material to an adjustable delivery tube which terminates with a nozzle. The nozzle delivers a low velocity controlled spray pattern which coincides with the stream of pressurized resin. The nozzle is positioned at an acute angle relative to the longitudinal axis of the resin stream and injects the dry lightweight particulate material into the stream. Within the venturi pump and opposite to the main low pressure, low volume inlet, is a second pressurized inlet. This inlet directly controls the degree of vacuum, thereby precisely determining the amount of dry lightweight particles delivered to the resin stream.