Plastic Material Selection for Injection Molding: ABS, PC, PP, PA, POM and More

The resin sets the shrinkage, the strength, the heat limit, the finish and a large part of the cost. Choose it early, because it drives mold design, steel choice and tolerance.

Quick answer

Start from the use, not the resin name. List the mechanical load, temperature, chemicals, UV exposure, appearance, regulatory needs and target price. Then shortlist: ABS for general housings, PC or PC/ABS for strength and heat, PP for chemical resistance and living hinges, PA (nylon) for wear and strength, POM for low-friction gears and precision parts, PBT for electrical parts, and PMMA for clarity. The data below is typical and general. Check the supplier datasheet for the exact grade.

Key takeaways

• Shrinkage differs by resin and fill, and it changes tolerance and warpage.
• Glass-filled grades increase stiffness but cause warpage and tool wear.
• Moisture-sensitive resins such as PA, PC and PBT must be dried before molding.
• Ask for RoHS and other documentation early if your market needs it.

Common resins at a glance

Resin	Strengths	Limits	Typical uses	Typical shrinkage*
ABS	Easy to mold, good surface, impact toughness	Lower heat and chemical resistance	Housings, consumer products	About 0.4 to 0.7%
PC	Strong, tough, good heat resistance, can be clear	Notch sensitive, needs drying, stress cracking with some chemicals	Covers, lenses, structural parts	About 0.5 to 0.7%
PC/ABS	Balance of PC strength and ABS processability	Cost, grade-dependent	Electronic housings	About 0.5 to 0.7%
PP	Chemical resistance, low cost, living hinges	Higher shrinkage, lower stiffness, hard to paint or bond	Containers, hinges, automotive interiors	About 1.0 to 2.0%
PA6 / PA66	Strong, wear resistant, good heat, often glass-filled	Absorbs moisture, dimensions change	Gears, brackets, functional parts	About 0.7 to 2.0%, depends on fill
POM	Low friction, stiff, dimensionally stable	Hard to bond, sensitive to some acids	Gears, bearings, precision parts	About 1.8 to 2.5%
PBT	Electrical properties, heat resistance, chemical resistance	Warps if unfilled, glass-filled common	Connectors, electrical housings	About 1.2 to 2.0%, depends on fill
PMMA	Optical clarity, scratch resistance	Brittle	Lenses, light guides	About 0.3 to 0.6%

*Typical ranges for general guidance only. Real shrinkage depends on grade, fill, wall thickness and process. Use datasheet values for design.

How to choose, step by step

1. Define the requirements: load, impact, temperature range, chemicals, UV, flame rating, food or skin contact, appearance and color.
2. Define the constraints: budget, volume, tolerance and the target market's regulations.
3. Shortlist two or three resins and compare datasheets, not marketing names.
4. Check processability: shrinkage, flow length, drying needs and gate sensitivity.
5. Test with samples from a prototype or rapid tool before locking the production resin.

Decision rules

• Need a good-looking housing at low cost: ABS, or PC/ABS if heat or strength is higher.
• Need a transparent part: PC for toughness, PMMA for clarity and scratch resistance.
• Need chemical resistance or a living hinge: PP.
• Need strength and wear resistance: PA, often glass-filled, and plan for moisture.
• Need precision and low friction: POM.
• Need electrical insulation and heat: PBT or glass-filled PA.

Fillers and additives

Additive	Effect	Watch for
Glass fiber	Higher stiffness and heat deflection	Anisotropic shrinkage and warpage, surface finish, faster tool wear
Flame retardants	Meet flame ratings	Possible mechanical loss, regulatory review
UV stabilizers	Outdoor durability	Cost and color effects
Colorants	Appearance	Color matching and batch consistency
Regrind	Lower material cost	Property loss, limits in regulated or cosmetic parts

Abrasive fillers, such as glass fiber, favor hardened tool steel. See mold steel choices.

Worked example (illustrative, not a customer project)

An outdoor sensor enclosure needs impact toughness, UV resistance, a flame rating and a good-looking surface. A sensible path: shortlist a UV-stabilized, flame-retardant PC/ABS and a UV-stabilized PC or ASA grade, compare datasheets for impact, heat deflection and flame rating, mold samples of both, expose them to your own tests and choose on results and price. Record the final grade name and supplier.

Validate before you lock the resin

• Sample parts molded in the intended resin and color
• Fit, assembly and snap-fit checks
• Heat, impact, chemical and UV tests relevant to the use
• Dimensional check after cooling, and after conditioning for moisture-sensitive resins
• Documentation for your market, such as RoHS statements

How resin affects the mold and the price

Resin drives shrinkage allowance in the tool, venting, gate design, cooling and cycle time, and these affect tooling cost and part cost. Read how mold cost is built up and hot runner vs cold runner, because some resins and colors suit one more than the other.

Compliance and documents

Many buyers need RoHS or other documentation. HC-Mold can provide RoHS and CE documentation on request, and the exact documents depend on your resin and product. State your market early so the right grade is quoted. Use the DFM checklist and read common molding defects to see how resin choice affects them.

What to send for a material recommendation

Part model and drawing, operating temperature range, chemical or UV exposure, appearance and color, regulatory requirements, annual volume and target cost. Injection molding at HC-Mold starts from 500 pcs: see MOQ by process. Free DFM review, mold-flow analysis and T0 trial and modification are included in the mold project.

FAQ

Which plastic is best for a general consumer housing?

ABS is a common starting point for appearance and cost. PC/ABS is used when more heat or strength is needed.

Why do some resins need drying?

PA, PC and PBT absorb moisture, which causes splay and weak parts when molded wet. Dry them per the datasheet.

Does glass fiber help or hurt?

It raises stiffness and heat resistance, but increases warpage risk and tool wear. It often needs hardened steel.

Can HC-Mold supply RoHS documents?

RoHS and CE documentation is available on request. The exact documents depend on the resin and the product.

How do I choose between PP and PA?

PP suits chemical resistance, living hinges and low cost. PA suits strength and wear, but absorbs moisture and changes dimensions.

Not sure which resin fits?

Send your part, its operating conditions and your target market. Engineers recommend two or three resin options under NDA. We reply within 12 hours.

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