Shrinkage & Warpage
The core side of the part can be designed with less regard for shrinkage if the mold maker and blow molder make the correct adjustments in the tool-building phase. The shrinkage of an interior pocket is restricted by the metal core used to form the pocket. Minor mold-metal removal can improve fit when this occurs. Overall the shrinkage of the interior will match the shrinkage of the exterior in the % range related to wall thickness discussed in the exterior shrinkage & warpage section.

Interior part design must consider the potential for warpage. Warp will be caused by variations in wall thickness and material distribution during cooling. Both W>2D overall sizing and W>D localized draw ratios need to be followed throughout the part design to prevent warpage.