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ENGINEERING GUIDE

Engineering Plastics & Material Selection Guide

Material selection for injection molding should not begin with a polymer name. It begins with the product requirements, operating environment, geometry, manufacturing process and the way the finished part will be validated.

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START WITH THE APPLICATION

Start with the application, not the polymer.

The same polymer family can contain grades that behave very differently. A useful material-selection process therefore starts by defining requirements rather than by choosing from a familiar list of resins. Temperature, load, chemicals, service life, human contact, tolerances, optics, sealing and regulatory requirements can all change both the material choice and the product and mold design.

Mechanical load and service life

Define sustained load, cyclic load, impact, threads, snap-fits and the expected service life.

Temperature and environment

Operating temperature, heat peaks, humidity, UV, chemicals, oils and cleaning agents can change the appropriate family and grade.

Dimensional stability

Tolerances, moisture uptake, creep, shrinkage and fiber orientation may matter more than a headline strength value.

Surface and optical requirements

Gloss, color, transparency, texture, flow marks and weld lines depend on both material behavior and flow design.

Regulatory and validation requirements

Medical, food-contact, flame or customer-specific requirements must be verified at exact grade and documentation level.

MATERIAL FAMILIES

Common material families and what they change in the design.

This is not a final material recommendation table. It is a framework for early comparison. Final selection should be based on a specific grade, current supplier datasheet, application conditions, part design, mold design and validation plan.

PP

Versatile, low-density polyolefin with useful chemical resistance
Why engineers consider it

Low density, good chemical resistance and broad design flexibility across many molded applications.

Design / processing considerations

Stiffness, creep, shrinkage and low surface energy can affect tolerances, bonding, printing and joining.

Typical application types

Housings, functional parts, caps, living hinges and industrial or consumer components.

HDPE / LDPE

Polyethylene families for chemical resistance and low moisture uptake
Why engineers consider it

A range from flexible to relatively stiff grades, good water resistance and attractive material economics.

Design / processing considerations

Relatively high shrinkage, creep and low surface energy need attention in design and downstream operations.

Typical application types

Containers, covers, chemical-service parts and applications requiring low moisture uptake.

ABS

Balanced stiffness, appearance and processability
Why engineers consider it

Good surface appearance, useful dimensional behavior and suitable finishing options in appropriate grades.

Design / processing considerations

Chemical and temperature resistance are grade-dependent; outdoor exposure requires an appropriate UV strategy.

Typical application types

Housings, visible parts, consumer products and industrial components.

PA6 / PA66

Nylons for strength, wear and elevated-temperature duty
Why engineers consider it

Useful mechanical performance, wear resistance and a broad range of reinforced grades.

Design / processing considerations

Moisture uptake changes dimensions and properties; fiber reinforcement increases anisotropy and tool wear.

Typical application types

Mechanical parts, brackets, gears, connectors and reinforced structural components.

POM

Low friction and good mechanical dimensional behavior
Why engineers consider it

Wear performance, stiffness, low friction and relatively good dimensional stability.

Design / processing considerations

Processing window, venting and joining or bonding limitations must be considered for the exact grade and application.

Typical application types

Gears, bearings, mechanisms, clips and moving components.

PC

Impact performance and optical options in suitable grades
Why engineers consider it

High impact resistance and transparent-grade availability, with many engineering variants.

Design / processing considerations

Stress cracking with certain chemicals, drying requirements and relatively high processing temperatures can be important.

Typical application types

Impact-resistant housings, transparent covers and engineering components.

PBT / PET

Engineering polyesters for dimensional, electrical and thermal requirements
Why engineers consider it

Stiffness, stability and many reinforced or electrical grades.

Design / processing considerations

Drying, crystallinity, shrinkage and reinforcement influence both processing and tolerances.

Typical application types

Connectors, electrical parts, sensor housings and mechanical components.

PMMA

Optical clarity and appearance
Why engineers consider it

High transparency and good appearance for optical and decorative parts.

Design / processing considerations

Lower impact resistance than some alternatives; stress, gating and visible flow behavior must be managed.

Typical application types

Windows, optical covers, light guides and visible components.

PC/ABS

Balanced impact, processability and appearance
Why engineers consider it

A practical combination for many engineering housings and structural covers.

Design / processing considerations

Temperature, chemical, flame and finish performance depend strongly on the exact grade.

Typical application types

Housings, electronics, automotive and industrial components.

TPE / TPU / TPV

Thermoplastic elastomer families
Why engineers consider it

Flexibility, soft touch, sealing and the ability to integrate elastic function into thermoplastic manufacturing.

Design / processing considerations

Hardness, compression set, bonding to a substrate and temperature/media resistance are highly grade-specific.

Typical application types

Seals, grips, overmolding, buffers and flexible features.

PPS

High-temperature and chemical-performance engineering polymer
Why engineers consider it

Thermal stability, chemical resistance and highly stable reinforced grades.

Design / processing considerations

Cost, processing temperature, abrasive fillers and tooling demands require an integrated process decision.

Typical application types

Industrial, electrical and elevated-temperature components.

PEEK

High-performance polymer for demanding combined requirements
Why engineers consider it

High-temperature, mechanical and chemical performance in suitable grades.

Design / processing considerations

High resin cost, high processing temperatures and equipment/tooling requirements must be justified by the application.

Typical application types

Specialized medical, industrial or mechanical applications where requirements support the cost.

PSU / PPSU / PEI

High-performance amorphous families for heat and specialized applications
Why engineers consider it

High-temperature capability, dimensional stability and family-specific performance options.

Design / processing considerations

Drying, processing temperatures, chemical environment and cost require precise grade selection.

Typical application types

Medical, electrical, fluid-handling and specialized engineering applications.

LCP

High flow and geometry stability in very small or thin-wall parts
Why engineers consider it

Excellent flow in thin sections and useful performance in micro-features.

Design / processing considerations

Strong anisotropy means flow direction and weld-line strategy should be addressed early.

Typical application types

Miniature connectors, electronics and thin-wall precision parts.

Why the grade matters more than the polymer family name

Two grades from the same polymer family may differ in reinforcement, viscosity, impact modification, UV package, flame rating, color package, regulatory documentation and processing window. A statement such as “PC” or “PA66” is therefore not a complete material specification. Selection should progress from family to a defined commercial grade, current datasheet, supply requirements and validation plan.

Reinforcement changes more than strength.

Glass fiber, mineral filler and other reinforcements can improve stiffness, creep and thermal behavior, but they also change flow, shrinkage, warpage, surface appearance, tool wear and properties relative to flow direction.

Fiber orientationPart properties are not necessarily equal in every direction. Gate location and flow pattern can affect strength, warpage and tolerances.
Tool wearReinforced compounds can increase wear at gates, runners, shut-offs and moving components, affecting steel and maintenance decisions.
Surface appearanceReinforcement type and loading can affect gloss, visible flow and the suitability of certain marking or finishing processes.
Shrinkage and warpageReinforcement may reduce average shrinkage while increasing directional differences. Geometry and tooling should account for this.

High-performance engineering plastics

When the requirement exceeds the practical range of common engineering resins, high-performance families may be considered. They are not universally “better”; they are justified when temperature, chemicals, mechanical load, sterilization, creep or packaging constraints genuinely require them.

PPS Temperature, chemical resistance and dimensional stability in suitable grades. High-temperature processing, frequent reinforcement, tool wear and cost.
PEEK Combined high temperature, mechanical and chemical requirements. Very high material cost and demanding processing/equipment conditions.
PPSU / PSU Heat capability, toughness and some cleaning or sterilization-intensive applications. Grade-specific compliance, drying, stress and chemical environment.
PEI Heat, dimensional stability, electrical properties and specialized grades. Processing temperature, chemical sensitivity and cost.
LCP Very thin sections, high flow and stability in small components. Anisotropy, weld lines and early flow-design decisions.

MATERIAL, MOLD & PROCESS

The material changes the mold, not only the part.

Material choice affects gates, runners, hot-runner strategy, cooling, venting, shrinkage allowance, draft, steel choice, polishing, wear and maintenance. Material Selection and Mold Design should therefore meet before geometry and tooling are frozen.

Flow and gate locationViscosity, fiber orientation and weld-line sensitivity affect gate position and how critical regions fill.
Cooling and mold temperatureCrystalline and amorphous materials, together with surface and tolerance requirements, demand different thermal strategies.
VentingMaterial, fill rate, additives and geometry can increase sensitivity to trapped gas, burn marks and incomplete filling.
Steel and wearReinforcement, flame-retardant packages and some additives can influence abrasion, corrosion risk and maintenance planning.
Shrinkage and dimensional strategyDatasheet shrinkage is only a starting point. Geometry, wall thickness, gate, pressure, fiber orientation and actual process determine the molded result.

Materials for Overmolding and 2K

In a multi-material system, each material working well alone is not enough. Exact grade compatibility, melt temperature, adhesion or mechanical interlock, shrinkage, stiffness mismatch, injection sequence and interface geometry all matter. General compatibility charts are useful for screening, but should not replace supplier data and validation of the actual grade pair and part.

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SPECIAL REQUIREMENTS

Medical, food contact, flame and other special requirements

A polymer family is not automatically “medical approved” or “food approved.” Suitability depends on the exact grade, color and additives, supplier documentation, target market, type of contact and sometimes the manufacturing and validation process.

Medical / biocompatibilityExact grade, supplier documentation, intended contact, sterilization method where relevant, change-control expectations and project-specific validation.
Food contactExact grade and color package, applicable jurisdiction and contact conditions; supplier declaration must match intended use.
Flame performanceExact UL or flammability classification, thickness dependency, color and any project-specific electrical or safety requirement.
UV / outdoorStabilization package, color, exposure duration and actual environment; “UV resistant” is not a universal material property.

SELECTION MATRIX

Material Selection Matrix: requirement to families commonly considered

Use this as a screening map, not as an automatic recommendation. The exact grade still has to satisfy the product, process, documentation and validation requirements.

Requirement Families commonly considered Engineering note
High impact PC, PC/ABS, modified PA, selected TPE/TPU Temperature, notch sensitivity and chemical environment can change the ranking.
High service temperature PBT/PET, PPS, PEI, PSU/PPSU, PEEK, selected PA grades Continuous-use temperature alone is not enough; load, aging and geometry matter.
Chemical resistance PP, PE, POM, PPS, PEEK and grade-specific engineering systems Check exact chemical, concentration, temperature and exposure time.
Low friction / wear POM, PA, PBT, PEEK and wear-modified grades Counterface, lubrication, pressure and speed are part of the material decision.
Dimensional stability POM, PBT, PPS, reinforced grades, LCP Moisture, fiber orientation, shrinkage and tool/process design remain critical.
Optical clarity PC, PMMA, selected transparent copolymers Optical quality depends on grade, wall, gate, polish, stress and molding conditions.
Flexible / sealing TPE, TPU, TPV, selected soft polyolefin systems Hardness, compression set, media exposure and substrate bonding must be checked.
Low density PP, PE and selected foamed or filled systems Weight target must be balanced against stiffness, creep and wall thickness.
Flame-retardant grades available PC/ABS, PBT, PA, PPS, PEI and other grade-specific systems The exact rating is grade-, thickness- and sometimes color-dependent.
Medical grades available PP, PC, ABS, TPE/TPU, PA, POM, PPSU, PEEK and others Only specific grades with the required documentation should be considered.
Food-contact grades available PP, PE, PET, selected PA/POM/TPE and others Compliance depends on exact grade, additives, color and jurisdiction.
Overmolding / 2K TPE/TPU over selected PP, PC/ABS, PA and other compatible substrate systems Use supplier compatibility data and validate the exact grade pair and interface geometry.
High stiffness Glass/mineral reinforced PA, PBT, PPS, PP, PEEK and other reinforced grades Higher stiffness can increase anisotropy, brittleness, warpage and tool wear.
Electrical performance PBT, PA, PC, PPS, PEI, LCP and grade-specific systems CTI, dielectric, flame and environmental requirements should be specified explicitly.

Cost is more than resin price.

Price per kilogram is only one part of total cost. A cheaper resin can require thicker walls, longer cycle time, more rejects, greater tool maintenance, secondary assembly or higher field risk. A more expensive resin can be the better choice when it reduces part count, weight, processing time or validation risk.

Part weightDensity and required wall thickness determine how much resin is actually purchased per part.
Cycle timeMelt and mold temperature, crystallization and cooling can dominate conversion cost.
Tooling and maintenanceAbrasive or demanding materials can change steel, hot-runner, maintenance and spare-part requirements.
Secondary operationsPainting, bonding, inserts, welding or assembly can outweigh a small difference in resin price.
Quality and validationProcess window, dimensional stability, documentation and validation effort are part of total cost and launch risk.

RELATED CAPABILITIES

Material selection connects directly to engineering and manufacturing.

Advanced Assembly & Automation Clean Room Injection Molding Engineering & DFM Industrial Design Injection Molding Molds Manufacturing Specialized Manufacturing Processes

Frequently Asked Questions

Can a material be selected from a property table alone?

No. A comparison table can narrow the field, but final selection should use a specific grade, the application conditions, geometry, manufacturing process and validation requirements.

What is the difference between a polymer family and a grade?

A polymer family is a broad chemical base. A grade is a defined commercial material whose molecular weight, reinforcement, modifiers, additives, color package and documentation can materially change performance and processing.

When should a reinforced material be considered?

When stiffness, creep, temperature or dimensional stability justify it. Warpage, fiber orientation, surface requirements and tool wear should be reviewed at the same time.

Is a medical or food-contact material defined by polymer type?

No. The exact grade and its relevant documentation must be verified for the target market, contact condition, color and intended use.

When should the mold maker be involved in material selection?

As early as possible when the material affects shrinkage, gating, venting, cooling, wear, hot-runner strategy, fiber orientation, surface requirements or tight tolerances.

MATERIAL SELECTION AS PART OF PRODUCT ENGINEERING

Have the product requirements, but not the material yet?

Send us the requirements, drawing or existing part. We can review material selection together with DFM, mold design, injection molding and the path to stable serial production.

Send Project Details Or call a project manager 052-2648136

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