Common Plastics Shrinkage Rate Overview

Plastic shrinkage rate is a core process parameter for injection mold design and product manufacturing, directly determining the accurate calculation of mold cavity dimensions, product dimensional stability and assembly precision. Different types of plastics vary significantly in shrinkage rate due to differences in molecular structure, crystallinity and modified formulations. In particular, crystalline plastics and non-crystalline plastics show obvious shrinkage gaps, while reinforced materials added with glass fiber and other fillers can greatly reduce shrinkage rate and improve anisotropy.

I. General Plastics

PE (Polyethylene): 1.5%–3.0% (LDPE 1.8%–2.5%, HDPE 1.5%–2.2%, LLDPE 1.6%–2.4%)

PP (Polypropylene): 1.0%–2.5% (homopolymer PP 1.5%–2.2%, copolymer PP 1.0%–1.8%)

PVC (Polyvinyl Chloride): 0.4%–0.8% (rigid PVC 0.5%–0.7%, flexible PVC 0.6%–1.0%)

PS (Polystyrene): 0.4%–0.7% (general-purpose PS 0.5%–0.6%, HIPS 0.5%–0.8%)

SAN (Styrene-Acrylonitrile Copolymer): 0.3%–0.6%

GPS (General-Purpose Polystyrene): 0.4%–0.7%

II. Engineering Plastics

ABS (Acrylonitrile-Butadiene-Styrene Copolymer): 0.4%–0.7% (general grade 0.5%–0.6%, reinforced grade 0.3%–0.5%)

PC (Polycarbonate): 0.5%–0.7% (general PC 0.6%, reinforced PC 0.2%–0.4%)

PET (Polyethylene Terephthalate): 1.2%–2.0% (unreinforced 1.5%–2.0%, reinforced grade 0.2%–0.6%)

PA6 (Polyamide 6): 1.5%–2.5% (unreinforced 1.8%–2.2%, reinforced grade 0.3%–0.8%)

PA66 (Polyamide 66): 1.0%–2.0% (unreinforced 1.2%–1.8%, reinforced grade 0.2%–0.6%)

POM (Polyoxymethylene): 1.8%–2.5% (homopolymer POM 2.0%–2.5%, copolymer POM 1.8%–2.2%)

PMMA (Polymethyl Methacrylate): 0.2%–0.8%

PBT (Polybutylene Terephthalate): 1.2%–2.0% (unreinforced 1.5%–1.8%, reinforced grade 0.3%–0.7%)

PPO (Polyphenylene Oxide): 0.5%–0.8% (unreinforced 0.6%–0.8%, reinforced grade 0.2%–0.4%)

PEN (Polyethylene Naphthalate): 0.8%–1.5% (reinforced grade 0.3%–0.5%)

III. Special Engineering Plastics

PEEK (Polyether Ether Ketone): 1.2%–1.8% (unreinforced 1.5%, reinforced grade 0.2%–0.5%)

PSU (Polysulfone): 0.5%–0.7%

PVDF (Polyvinylidene Fluoride): 1.0%–1.5%

LCP (Liquid Crystal Polymer): 0.1%–0.3% (low shrinkage, reinforced grade < 0.2%)

PPA (Polyphthalamide): 0.3%–0.8% (reinforced grade 0.2%–0.5%)

PTFE (Polytetrafluoroethylene): 2.0%–4.0%

IV. Thermoplastic Elastomers

TPU (Thermoplastic Polyurethane): 0.5%–1.5% (higher hardness means lower shrinkage)

TPE (Thermoplastic Elastomer): 0.8%–1.5%

TPR (Thermoplastic Rubber): 1.0%–2.0%

EVA (Ethylene-Vinyl Acetate Copolymer): 1.5%–3.0% (higher VA content means higher shrinkage)

V. Plastic Alloys

PC/ABS Alloy: 0.4%–0.6%

PC/PBT Alloy: 0.6%–1.0%

ASA (Acrylonitrile-Styrene-Acrylate Copolymer): 0.4%–0.7%

VI. Thermosetting Plastics

PF (Phenolic Plastic): 0.2%–0.8%

EP (Epoxy Resin): 0.1%–0.5% (< 0.3% with fillers)

UPR (Unsaturated Polyester Resin): 0.3%–1.0%

MF (Melamine-Formaldehyde Resin): 0.2%–0.6%

UF (Urea-Formaldehyde Resin): 0.3%–1.0%

Notes

The shrinkage rate refers to the conventional range for injection molding. The actual value is affected by formulation, molding process (temperature, pressure, cooling time) and product structure.

Reinforced materials (with glass/carbon fiber) have significantly lower shrinkage than unreinforced ones, and there is a difference (0.1%–0.3%) between the shrinkage along the flow direction and the vertical direction.