An integral PVC foam sheet is created with relatively high density near the surface and low density at the core. During calibration of the sheet, the cells at the surface are smoothed out. In the interior foaming process (Celuka), the entire surface of the profile is subjected to drastic cooling immediately after leaving the die. This suppresses the formation of cells on the surface of the extruded profile. Simultaneous calibration prevents further enlargement of the profile’s cross-section. In this process, foaming takes place mainly towards the core.

By optimal interaction between the PVC compound , foaming agent, perfect melt homogenizing and foam calibration can
excellent end product quality be achieved.