Thermoplastic Material Selection for Injection Molding: Past Datasheet Adjectives
Content in this Article
Thermoplastic cannot be selected from the highest datasheet value alone. Service temperature, load, chemical exposure, process and inspection method define the practical shortlist.
- Define function, environment, quantity and risk before selecting a material or process.
- Treat typical values as comparison points; confirm the exact grade and supplier capability before release.
- Use a first article or pilot lot to verify dimensions, function and records before scaling.
Define the decision
Document function, environment, quantity and risk so every option is compared against the same requirement.
Start With the Service Environment, Not the Property List
The right first question is not 'what are this resin's properties' but 'what will this part experience in service'. Temperature range, UV exposure, chemical contact, moisture, and mechanical load envelope define the feasible set.
| Environment | Key Property Filter | Typical Candidates | Typical Exclusions |
|---|---|---|---|
| Indoor consumer (20 – 40 °C) | Cost, moldability | ABS, PP, HIPS | - |
| Office / handheld electronics | Soft-touch pair, impact | PC/ABS, PC, ABS | POM (too slippery) |
| Automotive interior (-20 to 90 °C) | UV, heat distortion | PC/ABS, ASA, PP-EPDM | PS (crazes), unmodified PC |
| Automotive under-hood (to 125 °C) | Continuous-use temp | PA6/66 GF, PPA, PPS | PP, ABS, PC |
| Medical reusable | Steam/chemical resistance | PC (tested grades), PSU, PEI | Unmodified ABS |
Ten Common Material Families for Injection-Molded Parts
| Family | Tensile (MPa) | HDT 0.45 MPa (°C) | Moisture (% 24h) | Typical Cost Index |
|---|---|---|---|---|
| PP | 25 – 40 | 90 – 120 | <0.05 | 1.0× (baseline) |
| ABS | 35 – 55 | 85 – 105 | 0.2 – 0.4 | 1.3× |
| PC | 55 – 75 | 130 – 145 | 0.1 – 0.2 | 2.1× |
| PC/ABS | 50 – 65 | 105 – 125 | 0.15 – 0.3 | 1.8× |
| PA6/66 GF30 | 110 – 180 | 200 – 220 | 1.5 – 2.5 | 2.4× |
Thermoplastic evaluation flow
Define requirements, narrow the material and process, then verify with a consistent acceptance method.
- 1Requirements
Function, environment, quantity and risk
- 2Options
Material, process, design controls and finishing
- 3Acceptance
Dimensions, functional tests and production records
Compare the practical options
Compare material, process, design controls and finishing together—not unit price alone.
Heat Distortion Temperature Is the Single Most Abused Number
HDT is reported at two loads — 0. 45 MPa and 1.
Validate before scaling
Before scaling, verify dimensions, function and records with one controlled method across representative lots.
UV Stability: The Property That Fails in Month 14
Unmodified ABS, PS, and PP go chalky, yellow, and brittle under sustained UV in 6 – 18 months. Outdoor-rated grades add UV stabilisers and HALS packages that push life to 5 – 10 years.
Pre-RFQ review: recommended practice and common mistakes
| Recommended practice | Common mistake |
|---|---|
| Document function, environment, quantity and risk | Select from a material name or machine specification alone |
| Review material, process, design controls and finishing together | Address manufacturing limits only after design freeze |
| Inspect critical dimensions and function on the first article | Scale production from visual approval alone |
| Keep material, revision and inspection records | Reuse old results after a material or process change |
- Function, environment, quantity and risk are documented
- Material, process, design controls and finishing are reviewed with the supplier
- Critical dimensions, appearance and functional acceptance are on the drawing or RFQ
- First-article or pilot-lot verification is planned
- Material, process and revision changes trigger a new review
FAQ, further reading and sources
What should be defined first for Thermoplastic?
Start with function, environment, quantity and acceptance criteria. These inputs narrow the practical options faster than naming a machine or material first.
Can typical values in this article be released directly on a drawing?
No. Use them for early comparison, then confirm the exact grade, supplier capability and first-article result.
When is the process ready to scale?
Scale only after material, process, finishing and inspection are controlled and repeatable across representative lots.
Next, explore 3D printing services, CNC machining, materials, and the related reports linked on this page.
