Polymer Composition and Material Properties:
The degree of shrinkage depends on the polymer’s molecular weight, viscosity, and crystallization behavior. A higher molecular weight and viscosity result in a higher degree of shrinkage, while crystallization behavior affects the shrinkage rate. Crystallizable polymers have a higher tendency to shrink than non-crystallizable polymers.

Additionally, additives such as fillers, fibers, and stabilizers can affect the shrinkage behavior of the polymer. Thus, it is crucial to select the appropriate material based on the desired shrinkage characteristics.

Processing Conditions Applied:
The processing conditions applied in plastic injection molding can also affect shrinkage. The temperature, pressure, and cooling time all impact the shrinkage behavior of the molded part. 

Higher temperatures and pressures result in a higher degree of shrinkage, while longer cooling times lead to a slower rate of shrinkage. Thus, it is important to carefully select and optimize the processing conditions to avoid a shrinkage problem in injection molding.

Part Design and Geometry:
Part design and geometry, such as the thickness of the walls, the size and location of ribs, and the presence of sharp corners or edges can all impact the shrinkage behavior of the part. Thin walls, which are popular in medical plastic injection molding may experience a higher degree of shrinkage, resulting in warpage or distortion.

Additionally, the placement and design of gates and vents can impact the shrinkage behavior of the molded part. It is important to optimize the part design and geometry to minimize the degree of shrinkage and achieve the desired dimensions and tolerance.