There are many types of materials that may be used in the injection molding process. Most polymers may be used, including all thermoplastics, some thermosets, and some elastomers. When these materials are used in the injection molding process, their raw form is usually small pellets or a fine powder. Also, colorants may be added in the process to control the color of the final part. The selection of a material for creating injection molded parts is not solely based upon the desired characteristics of the final part. While each material has different properties that will affect the strength and function of the final part, these properties also dictate the parameters used in processing these materials. Each material requires a different set of processing parameters in the injection molding process, including the injection temperature, injection pressure, mold temperature, ejection temperature, and cycle time. A comparison of some commonly used materials is shown below

 Plastic mold steel Products include S-7 grade mold steel, P-20 grade pre-hardened mold steel, 420SS grade stainless steel, 

XPS                Polystyrene Crystal

HIPS               High Impact Polystyrene

 SAN                Styrene Acrylonitrile Copolymer

 ABS                Acrylonitrile Butadiene Styrene

 PMMA             Polymethylmethacrylate (Acrylic)

 MBS               Polymethacrylate Butadiene Styrene

 RPVC              Rigid Polyvinyl Chloride

 CPVC              Chlorinated Polyvinyl Chloride

 PVDC              Polyvinylidene Chloride

 PB                  Polybutylene

 LDPE              Low Density Polyethylene

 LLDPE             Low Linear Density Polyethylene

 HDPE              High Density Polyethylene

 HMWHDPE     High Molecular Weight HDPE

 LCP                Liquid Crystal Polymer

 PAS                Polyarylsulfone

 PAEK              Polyaryletherketone

 PC/ABS           Polycarbonate/ABS Alloy

 PEEK              Polyetheretherketone

 PEI                 Polyetherimide

 PEKEKK          Polyetherketoneetherketoneketone

 PES                Polyethersulfone

 POM               Acetal

 PPA                Polyphtalamide

 PPE                Phenylene Ether Copolymer

 PPS                Polyphenylene Sulfide

 PSO                Polysulfone

 PUR                Polyurethane Plastic Rigid

 TPI                 Polyimide

 PP                  Polypropylene Homopolymer

 PP/Co             Polypropylene Copolymer

 PP/Talc           Polypropylene 40% Talc Filled

 PP/Glass f       Polypropylene 30% Glass Filled

 EVA                Ethylene Vinyl Acetate

 In Ionomers    (Surlyn)

 CP                   Cellulose Acetate Propionate

 TPU                Thermoplastic Polyurethane

 TPO                Thermoplastic Elastomer Polyolefin

 TP                   Thermoplastic Elastomer Polyester

 PA6                 Polyamide     (Nylon) 6

 PA66               Polyamide     (Nylon) 66

 PA11               Polyamide     (Nylon) 11

 PA12G            Polyamide 12,     30% glass filled

 PA66M            Polyamide 66,     40% mineral filled

 PBT                Polybutylene Terephtalate

 PET                Polyethylene Terephtalate

 PETG              Polyethylene Terephtalate Glycol

 PC                   Polycarbonate

 PVDF              Polyvinyldene Fluoride

Automatic Injection Moulds,

Compression Moulds,

Hot Runner / Semi Hot Runner Moulds,

Hydraulic Core Puller System Moulds,

Rotational Core System Moulds,

Automatic Split Injection moulds,

Die, Jigs & Fixtures,

Plastic Mould Design,

Plastic Products Design,

Metal Injection Mould,

Plastic Injection Molded Components,

CNC  Precision Machining.

Plastic Shrinkage rate is a volume contraction rate of polymers from the melt state and the cooled condition that will determine the molding parts dimension and accuracy, it is expressed in percent.
Semi-crystalline polymers (e.g: PBT or PP) always show a higher shrinkage than amorphous polymers (e.g: PS or PC) because when cooled down semi-crystalline polymers will see part of their macromolecular chains re-arranged to form crystallite, that is a well-organized structure, leading to less space needed for the same amount of atoms. This volume contraction of polymers often leads to wrapped parts and dimension differences between manufactured parts and the mold (the die if we consider extrusion as the processing technique).
Plastic shrinkage rate is strongly depending on the polymer itself but also on the processing conditions applied and part design. A standard method to measure “molding plastic shrinkage”, ie contraction compared to the injection molding tool, is the ASTM D955. Other international standard methods related to plastic shrinkage are ISO 294-4 (for thermoplastics) and ISO 2577 (for thermosets).