A filling head comprising: a housing having a lower nozzle exit, a first material inlet, a second material inlet and a reciprocatable piston movable within the housing; the piston having a) an outer wall and upper and lower ends; b) a first internal material flow channel connecting an entry in the outer wall to an exit in the lower end, c) a second internal material flow channel connecting an entry in the outer wall to an exit in the lower end, and; wherein the exit of the first channel is annular, surrounding the exit of the second material flow channel; the piston, housing and inlets being positioned and dimensioned such that the piston in relation to the housing has: (1) an upper position wherein material flows from both first and second inlets are blocked by the piston outer wall; (2) a mid position wherein the first material inlet is in communication with the first internal material flow channel entry but the second material inlet is blocked by the piston outer wall; (3) a lower position wherein the first material inlet is in communication with the first internal material flow channel entry and the second material inlet is in communication with the second internal material flow channel entry.