Plastic Material Shrinkage Rates

Plastic moulding shrinkage is the contraction of a plastic moulding as it cools after injection. Most shrinkage occurs in the mould during cooling, but some shrinkage occurs after ejection, as the part continues to cool. After that, the part may continue to shrink very slightly for several hours or even days until the temperature and moisture content stabilise.

All polymers have different shrink rates depending on many factors. These include amorphous or crystalline materials, cycle times, temperatures, mould design, part shape and wall thickness.

Our chart shows typical shrinkage ratios for the list of materials