Plastic Composition: The type of plastic used for injection molding can greatly affect the shrinkage of the final product. For example, high-density polyethylene mold shrinkage is due to its crystalline structure, which causes the polymer chains to contract during cooling.

Molecular Weight: Higher molecular weight polymers tend to shrink less than lower molecular weight polymers because they have more intermolecular forces holding them together.

Additives: Additives such as fillers, colorants, and lubricants can also affect the mold shrinkage of plastic parts. For example, adding a filler material can increase the stiffness of the plastic, which results in higher shrinkage during cooling.

Stress Level: During the injection molding process, the time and pressure at which the part is placed under stress cause an excessive amount of fluid, which leads to shrinkage and brittleness. And if the plastic is subjected to high levels of stress during cooling, it can cause the polymer chains to rearrange and contract, resulting in higher shrinkage.