Injection molding apparatus for making an article comprising: - a mold body having an inner surface defining a main cavity apt in use to contain primary molten polymeric material, wherein said main cavity comprises a first region apt to receive a first fraction of said primary molten polymeric material and a second region (12") apt to receive a second fraction of said primary molten polymeric material; - a first tank in fluid communication with said main cavity by means of a first mouth passing through said inner surface and apt in use to contain auxiliary molten polymeric material; - a first pressurized gas injector, said first injector being in communication with said first tank and configured to inject said pressurized gas into said first tank to displace at least part of said auxiliary molten polymeric material from said first tank into said main cavity and wherein said first pressurized gas injector comprises a first nozzle having an outlet completely contained within said first tank in order to inject or push the auxiliary molten polymeric material into the main cavity in such a way that at least part of said auxiliary molten polymeric material acts as a barrier against an entry of said pressurized gas into the main cavity; and wherein said injection molding apparatus further comprises: - a second tank in fluid communication with said main cavity by means of a second mouth passing through said inner surface and apt in use to contain auxiliary molten polymeric material; - a second pressurized gas injector, wherein said second injector comprises a second nozzle having an outlet completely contained within said second tank such that said second injector is in communication with said second tank to inject the pressurized gas into said second tank to displace at least part of the auxiliary molten polymeric material from said second tank into said main cavity in such a way as to prevent an entry of said pressurized gas into the main cavity; wherein said first tank is in fluid communication with said first region and said second tank is in fluid communication with said second region (12") and wherein said first mouth and said second mouth are arranged substantially one in front of the other or so as to face each other. - a mold body having an inner surface defining a main cavity apt in use to contain primary molten polymeric material, wherein said main cavity comprises a first region apt to receive a first fraction of said primary molten polymeric material and a second region (12") apt to receive a second fraction of said primary molten polymeric material; - a first tank in fluid communication with said main cavity by means of a first mouth passing through said inner surface and apt in use to contain auxiliary molten polymeric material; - a first pressurized gas injector, said first injector being in communication with said first tank and configured to inject said pressurized gas into said first tank to displace at least part of said auxiliary molten polymeric material from said first tank into said main cavity and wherein said first pressurized gas injector comprises a first nozzle having an outlet completely contained within said first tank in order to inject or push the auxiliary molten polymeric material into the main cavity in such a way that at least part of said auxiliary molten polymeric material acts as a barrier against an entry of said pressurized gas into the main cavity; and wherein said injection molding apparatus further comprises: - a second tank in fluid communication with said main cavity by means of a second mouth passing through said inner surface and apt in use to contain auxiliary molten polymeric material; - a second pressurized gas injector, wherein said second injector comprises a second nozzle having an outlet completely contained within said second tank such that said second injector is in communication with said second tank to inject the pressurized gas into said second tank to displace at least part of the auxiliary molten polymeric material from said second tank into said main cavity in such a way as to prevent an entry of said pressurized gas into the main cavity; wherein said first tank is in fluid communication with said first region and said second tank is in fluid communication with said second region (12") and wherein said first mouth and said second mouth are arranged substantially one in front of the other or so as to face each other. - a second tank in fluid communication with said main cavity by means of a second mouth passing through said inner surface and apt in use to contain auxiliary molten polymeric material; - a second pressurized gas injector, wherein said second injector comprises a second nozzle having an outlet completely contained within said second tank such that said second injector is in communication with said second tank to inject the pressurized gas into said second tank to displace at least part of the auxiliary molten polymeric material from said second tank into said main cavity in such a way as to prevent an entry of said pressurized gas into the main cavity;