Engineering-grade plastics are thermoplastic resins we turn to when an application needs more temperature resistance, dimensional control, mechanical performance, or processing control than a commodity resin can deliver. ABS, polycarbonate (PC), nylon, and PBT are the four resin families we classify as engineering-grade; PEEK, PEI, and PPA move into consideration when an application’s temperature, chemical, or dimensional requirements go further still.
Commodity resins like PP, PE, and general-purpose polystyrene hold up fine in plenty of applications. Sustained heat, moisture exposure, chemical contact, or repeated mechanical stress in the field is usually where they start to fall short—and that’s the point where we see customers move toward an engineering-grade resin, often PC or nylon, to protect long-term part reliability rather than just clear a bench test.
Selecting the right grade takes more than comparing a couple of performance numbers. Application temperature, moisture exposure, mechanical load, dimensional tolerances, and processing requirements all affect which resin will actually hold up. This guide walks through the processing and shrinkage data behind our four core engineering resins, plus the PEEK, PEI, and PPA crossover tier, pulled directly from our own Injection Molding General Processing Ranges and Plastic Injection Molding Material Shrinkage Guide.
QTM sources commodity, engineering, and high-performance thermoplastic resins and supports custom color and compound formulation, reinforced-grade sourcing, and material selection, including consulting on resin choice for harsh-environment applications where a commodity resin won’t hold up over the life of the part. The data below is a starting point for that comparison, before a material is specified or tooling is finalized.
What Are Engineering-Grade Plastics?
Engineering-grade plastics are selected for applications with requirements beyond the typical processing and performance range of commodity resins. The distinction affects how the material must be processed as well as how the finished part performs.
Moisture control is one example. PC requires drying at 250°F for four hours, with maximum moisture content below 0.02%, about five times tighter than ABS’s 0.10% threshold. Nylon 6 and Nylon 66 have a maximum moisture content of 0.20% and readily absorb moisture. Excess moisture during molding can cause hydrolytic degradation, reducing part strength and creating inconsistent performance.
Shrinkage also differs between resin families. PE has a mold shrinkage range of .015–.035 in./in., while PP ranges from .010–.025 in./in. PC has a range of .003–.007 in./in. Reinforced Nylon 66 ranges from .003–.005 in./in.
These values affect dimensional planning and tooling. A resin with a wider shrinkage range may require different tooling considerations than one with tighter shrinkage characteristics.
Engineering-Grade vs. Commodity Plastics
Commodity plastics such as PE and PP are commonly used when the application can operate within their temperature, mechanical, and dimensional performance ranges. They also tend to have less demanding processing requirements.
Engineering-grade plastics become more relevant when an application requires tighter dimensional control, higher operating temperatures, greater mechanical performance, or closer control of moisture and processing conditions.
Material selection should be based on the conditions the finished part will encounter. Prototype performance under controlled conditions doesn’t necessarily predict how a material will perform after exposure to sustained temperature, moisture, chemical exposure, or repeated mechanical loads.
ABS: Processing and Shrinkage
ABS is one of the less demanding engineering resins in terms of processing requirements. It dries at 180°F for three hours, with maximum moisture content below 0.10%.
Mold shrinkage ranges from .003–.007 in./in. in our Processing Ranges guide. Our separate Shrinkage Guide lists .004–.008 in./in. for ABS.
Recommended tonnage is 2.5–3.5 tons per square inch—the lowest recommended tonnage range among the standard engineering resins in this guide.
The combination of moderate drying, moderate shrink, and the lowest tonnage requirement of the group is often why ABS gets specified first when a part’s demands are real but not extreme.
Polycarbonate (PC): Processing and Shrinkage
PC requires tighter moisture control than ABS. The recommended drying cycle is 250°F for four hours, with maximum moisture below 0.02%.
Melt temperature ranges from 550–600°F for unreinforced PC and 600–650°F for reinforced grades. Recommended tonnage is 4.0–5.0 tons per square inch.
Unreinforced PC has a mold shrinkage range of .003–.007 in./in. Reinforced PC narrows to .001–.005 in./in.
Reinforced and unreinforced PC don’t just differ in stiffness; they call for different shrink allowances in the tool, which is why the grade needs to be locked in before cutting steel, not after.
Nylon: Moisture, Processing, and Shrinkage
Moisture control is a key processing consideration for nylon. Both Nylon 6 and Nylon 66 have a maximum moisture content of 0.20%, and both readily absorb moisture.
Nylon 6 has a mold shrinkage range of .010–.015 in./in. unreinforced and .003–.007 in./in. reinforced. Nylon 66 ranges from .012–.020 in./in. unreinforced and .003–.005 in./in. reinforced.
Our Shrinkage Guide also lists different recommended tonnage ranges for filled and unfilled nylon—3.0–4.0 unfilled versus 4.0–5.0 filled—another processing difference worth factoring into material selection.
That’s enough of a shift to make the fill decision worth settling early, before a part’s tolerance gets locked around the wrong number.
PBT: Processing and Dimensional Stability
PBT has drying requirements similar to PC. It’s dried at 250°F for three to four hours, with maximum moisture below 0.02%.
Unreinforced PBT has a mold shrinkage range of .017–.023 in./in. Reinforced PBT ranges from .003–.006 in./in.
Melt temperature ranges from 460–500°F for unreinforced PBT and 480–525°F for reinforced grades.
PBT’s unreinforced shrinkage posts the highest values in this guide, up to .023 in./in., which is often reason enough to specify a reinforced grade even when raw strength isn’t the deciding factor.
The figures in these sections describe processing and shrinkage behavior. Mechanical and thermal properties such as tensile strength, flexural modulus, notched Izod impact, and heat deflection temperature vary by manufacturer and grade. Confirm those values against the supplier’s data sheet before selecting a material for production.
PEEK, PEI, and PPA: When to Consider Higher-Performance Resins
PEEK, PEI, and PPA appear on our materials list in both the engineering and high-performance categories. We typically bring these into the conversation when an application’s requirements exceed what the standard engineering resins can hold.
Our Shrinkage Guide lists PEEK at 4.0–5.0 tons per square inch with a shrinkage range of .010–.020 in./in. PEI is listed at 3.0–4.0 tons per square inch with .005–.007 in./in. shrinkage. PPA is listed at 3.5–4.5 tons per square inch with .005–.007 in./in. shrinkage.
These three materials appear in our Shrinkage Guide but not our Processing Ranges document, so confirm drying temperatures, drying times, and melt temperatures against the supplier’s data sheet for the specific grade you’re evaluating.
How Does Reinforcement Affect Resin Selection?
Reinforcement changes mold shrinkage across the engineering resin families in our Processing Ranges guide.
Nylon 6 decreases from .010–.015 in./in. unreinforced to .003–.007 in./in. reinforced. Nylon 66 decreases from .012–.020 in./in. to .003–.005 in./in. PBT changes from .017–.023 in./in. unreinforced to .003–.006 in./in. reinforced. PC changes from .003–.007 in./in. to .001–.005 in./in. when reinforced.
Our Shrinkage Guide also provides separate tonnage recommendations for filled and unfilled nylon—3.0–4.0 unfilled versus 4.0–5.0 filled.
Reinforcement affects both material performance and processing considerations. For a part with tight dimensional requirements, we’d want to know the expected shrinkage of the specific reinforced or unreinforced grade before tooling is finalized.
What Should You Look for on a Resin Data Sheet?
Several processing values can help identify differences between resin families before a material reaches the mold:
- Drying temperature and time
- Maximum moisture content
- Mold temperature range
- Melt temperature range
- Mold shrinkage
Moisture content requires particular attention with PC, PBT, and nylon. Processing material above the recommended moisture level can cause hydrolytic degradation, which can reduce strength and create inconsistent part performance.
Actual shrinkage depends on wall thickness, gate location and size, tool configuration, cooling layout, and processing conditions. Use these ranges to compare resin families, then confirm grade-specific shrinkage and processing requirements against the supplier’s data sheet before finalizing tooling.
How We Support Engineering-Grade Resin Selection
Material data only gets you so far. Sourcing, grade availability, and how a resin will behave in the application still require conversation. Our sales and technical team brings more than 125 years of combined experience across engineering, commodity, and high-performance thermoplastics, and a good part of that experience sits in exactly the applications where commodity resins run out of room: parts exposed to sustained heat, moisture, or repeated mechanical stress in the field, where PC and nylon are the materials we’re asked to weigh in on most often.
We don’t mold parts. Our role is the material side of the project, identifying resin options, comparing processing requirements, and flagging where a grade needs to change before it’s locked into a drawing or a tool.
For processors and OEMs evaluating an engineering-grade resin, a review like this can surface changes in drying requirements, shrinkage, reinforcement, or other processing considerations before they become production problems.
Frequently Asked Questions About Engineering-Grade Plastics
What are engineering-grade plastics?
Engineering-grade plastics are thermoplastic resins used for applications that require performance or processing characteristics beyond typical commodity resins. Common examples include ABS, PC, nylon, and PBT.
When should I consider an engineering-grade resin?
Consider an engineering-grade resin when the application requires properties or processing control that a commodity resin can’t provide. Temperature exposure, moisture, mechanical loads, chemical exposure, and dimensional tolerances are all relevant factors.
How does reinforcement affect resin selection?
Reinforcement can reduce mold shrinkage and change recommended processing conditions. Our data shows lower shrinkage ranges for reinforced PC, nylon, and PBT compared with their unreinforced counterparts. The specific effect depends on the resin and grade.
What information should I compare on a resin data sheet?
Drying temperature and time, maximum moisture content, mold temperature, melt temperature, and mold shrinkage are useful starting points for comparing processing requirements. Mechanical and thermal properties should also be reviewed based on the application.
Does QTM mold parts?
No. We supply and source thermoplastic resin and support material selection, custom compounding, reinforced-grade sourcing, and processing guidance.
Need Help Selecting an Engineering-Grade Plastic?
Selecting a resin takes more than identifying a material that meets a single performance requirement. The grade also needs to match the application’s temperature range, dimensional requirements, moisture exposure, processing conditions, and production requirements.
We can review your current material specification, compare engineering-grade resin options, and identify processing or tooling considerations tied to a material or grade change.
Ready to review your material options? Contact us today.