The invention comprises a self-cleaning injection system for injecting foamable compositions into packaging applications. The system comprises an injection nozzle having an opening in one end from which mixed foam precursors which form foamable compositions may exit. The one end comprises a tip assembly which is porous to gases and to certain liquids, but which is impermeable to other materials such as the foamable compositions which may otherwise exit the housing only through said opening. A pump assembly pumps cleaning solvent from a solvent container to the injection nozzle while maintaining a constant delivery of air or a mixture of air and solvent to the injection nozzle. The pump assembly comprises a solvent container and an air compressor for sending air to the solvent container and for sending a mixture of solvent and air from the solvent container to said injection nozzle. The pump assembly is in communication with the injection nozzle so that a mixture of air and solvent may be sent from the solvent container to the pump assembly, to the injection nozzle and out of the porous tip assembly, to thereby help to clean accumulated foamable composition from the injection nozzle.