Category: Injection Molding Reading time: 10 min Meta description: A complete guide to injection molding materials — comparing ABS, PP, PC, nylon, POM, PMMA, and more. Learn which plastic suits your application and budget. URL: /blog/injection-molding-materials/ Tags: injection-molding, materials, plastics, engineering, selection
There are over 25,000 plastic grades available for injection molding. Choosing the wrong one leads to failed parts, delayed production, and wasted tooling investment.
This guide walks through the most common injection molding materials — what they're good for, what they're not, and how to choose based on your part's requirements.
Before selecting a material, answer these questions:
| Question | Why It Matters |
|---|---|
| What is the operating temperature? | Determines thermal class, heat deflection temperature |
| Is the part load-bearing? | Determines mechanical strength requirements |
| Will it be outdoors or in UV? | Determines weatherability needs |
| Is it exposed to chemicals? | Determines chemical resistance requirements |
| Does it need to be food-safe? | Narrows to FDA-approved grades |
| Does it need to be transparent? | Narrows to PC, PMMA, PS, or clear ABS |
| What is the target unit cost? | Higher-performance materials cost more |
| What surface finish is required? | Some materials polish better than others |
The most widely used injection molding plastic for a reason.
| Property | Value |
|---|---|
| Tensile strength | 40-50 MPa |
| Heat deflection (HDT) | 90-100°C |
| Impact (Izod) | 200-400 J/m |
| Shrinkage | 0.4-0.7% |
| Relative cost | $ (low) |
Best for: Enclosures, housings, consumer goods, toys, automotive interior trim. Avoid for: High-temperature environments, outdoor exposure without UV stabilization. Processing: Easy. Wide processing window, good flow. Surface finish: Excellent — can be textured, painted, plated.
| Property | Value |
|---|---|
| Tensile strength | 25-40 MPa |
| Heat deflection | 85-100°C |
| Chemical resistance | Excellent |
| Shrinkage | 1.5-2.5% |
| Relative cost | $ (low) |
Best for: Food containers, living hinges, chemical tanks, battery cases, automotive bumpers. Avoid for: UV exposure without additives, high-load applications. Processing: Good flow, but high shrinkage requires attention in mold design. Key advantage: Outstanding fatigue resistance — PP living hinges can flex millions of cycles.
Available in HDPE and LDPE grades.
| Property | HDPE | LDPE |
|---|---|---|
| Tensile strength | 25-35 MPa | 8-20 MPa |
| Flexibility | Stiff | Flexible |
| Chemical resistance | Excellent | Good |
| Application | Bottles, tanks, crates | Caps, flexible parts |
Best for: HDPE for bottles, containers, crates, cutting boards. LDPE for caps, lids, squeeze bottles.
| Property | Value |
|---|---|
| Tensile strength | 60-70 MPa |
| Heat deflection | 130-140°C |
| Impact resistance | 600-900 J/m (highest) |
| Transparency | Excellent (clear) |
| Shrinkage | 0.5-0.7% |
| Relative cost | $$ (moderate) |
Best for: Safety glasses, bulletproof glazing, medical devices, electronic housings, power tool bodies. Avoid for: Chemically aggressive environments, parts requiring UV resistance without coating. Processing: Requires drying (pre-dry at 120°C for 4+ hours). Higher viscosity, narrow processing window. Key advantage: Exceptional impact strength — virtually unbreakable in thin sections.
| Property | Value |
|---|---|
| Tensile strength | 50-85 MPa |
| Heat deflection | 65-80°C (dry) 180-240°C (glass-filled) |
| Wear resistance | Excellent |
| Chemical resistance | Good (oils, fuels) |
| Shrinkage | 0.8-1.5% |
| Relative cost | $$ (moderate) |
Best for: Bushings, gears, bearings, fasteners, under-hood automotive parts, power tool housings. Avoid for: Parts requiring tight dimensional stability — nylon absorbs moisture and swells (up to 2-3%). Processing: Must be dried before molding. Moisture content must be below 0.2%. Key advantage: Self-lubricating, excellent wear resistance.
| Property | Value |
|---|---|
| Tensile strength | 60-75 MPa |
| Heat deflection | 100-120°C |
| Coefficient of friction | 0.2-0.35 (low) |
| Shrinkage | 1.5-2.5% |
| Relative cost | $$$ (moderate-high) |
Best for: Precision gears, sliding mechanisms, mechanical parts, fuel system components, zippers. Avoid for: Outdoor UV exposure, acidic environments. Processing: Excellent dimensional stability. Low creep. Can flash easily — good mold venting required. Key advantage: Outstanding fatigue resistance and low friction — ideal for moving parts.
| Property | Value |
|---|---|
| Tensile strength | 50-70 MPa |
| Heat deflection | 85-95°C |
| Light transmission | 92% (best) |
| Shrinkage | 0.3-0.7% |
| Relative cost | $$$ (moderate-high) |
Best for: Optics, lenses, light guides, aquariums, display cases, auto tail lights. Avoid for: Impact-prone applications (brittle), high-temperature environments. Processing: Requires drying. High melt viscosity. Prone to sink marks in thick sections. Key advantage: Best optical clarity among thermoplastics — transmits 92% of visible light.
| Property | Value |
|---|---|
| Tensile strength | 90-100 MPa |
| Continuous use temp | 250°C |
| Chemical resistance | Excellent (almost universal) |
| Shrinkage | 0.5-1.0% |
| Relative cost | $$$$$ (very high — $100-200/kg) |
Best for: Medical implants, aerospace components, oil & gas seals, semiconductor equipment. Avoid for: Cost-sensitive applications (use PPS or PAI as alternatives). Key advantage: Highest-performance injection molding plastic — handles extreme temperature and chemical environments.
| Property | Value |
|---|---|
| Tensile strength | 55-85 MPa |
| Heat deflection | 130-200°C |
| Chemical resistance | Excellent |
| Flammability | V-0 (self-extinguishing) |
| Relative cost | $$$$ (high) |
Best for: Automotive under-hood electrical, pump housings, chemical processing equipment, electronics.
| Material | Cost ($/kg) | Typical Usage | Mold Shrinkage |
|---|---|---|---|
| PP | $1-2 | High volume, low cost | 1.5-2.5% |
| ABS | $2-3 | General purpose | 0.4-0.7% |
| HDPE | $1-2 | Packaging | 1.5-3.0% |
| PA6 (nylon) | $3-5 | Mechanical parts | 0.8-1.5% |
| PC | $4-6 | High impact | 0.5-0.7% |
| POM (acetal) | $4-6 | Precision sliding | 1.5-2.5% |
| PMMA (acrylic) | $4-6 | Optics | 0.3-0.7% |
| ABS+PC blend | $4-5 | Tough enclosures | 0.5-0.7% |
| PPS | $10-15 | High temp chemical | 0.2-0.5% |
| PEEK | $100-200 | Extreme performance | 0.5-1.0% |
| If you need... | Choose... | Why |
|---|---|---|
| Lowest cost, general purpose | PP or ABS | Best balance of cost and performance |
| High impact strength | PC | 10x the impact of ABS |
| Transparent part | PC (tough) or PMMA (optical) | Different trade-offs |
| Wear resistance, low friction | POM or PA6 | Self-lubricating |
| Chemical resistance | PP or PPS | Resist most solvents |
| High temperature (>150°C) | PPS or PEEK | Continuous use capability |
| Food contact | PP, PE, PET | FDA-approved grades |
| Outdoor UV exposure | ASA or ASA+PC | Won't yellow |
| Living hinge | PP | Fatigue life of millions |
| Precision, low shrinkage | PC or POM | Dimensional stability |
Not sure which material to use for your part? Start a conversation with our material advisor on app.moldkey.com/quote and get a material recommendation with price estimate.