Engineering Plastic Compounds
Reinforced and flame-retardant engineering compounds for moulders and OEMs: conditioned properties, flammability files and part-level trials.
Buyer summary
- What it is
- Reinforced, filled and flame-retardant compounds of engineering polymers (for example polyamides, PBT and POM) for moulded parts.
- Main applications
- Automotive under-hood and structural parts, electrical connectors and housings, appliance parts, power tools, gears and bearings, fluid-handling and building hardware.
- Critical purchasing specifications
- Polymer, reinforcement and filler content
- Conditioned (not only dry) mechanical properties, with methods (ISO 527 or ASTM D638)
- Heat deflection temperature, with its stated load (ASTM D648)
- Flammability listing for the exact grade, colour and thickness
- Change notification, including compounding-site changes
- Qualification considerations
- Fibre orientation, weld lines and moulding conditions make parts behave differently from test bars. An "equivalent" grade must be proven in the part.
- First step
- Give the part, the loads, the temperatures and the flammability requirement.
- How PAXOMER can assist
- Engineering compounds are qualified on conditioned properties in the moulded part, not dry datasheet values. PAXOMER can help define the part, load, temperature and flammability requirements, identify compounders with suitable grades and documentation, and coordinate trial lots for moulding and part testing. Commercial discussions can then be held at manufacturer level. Manufacturer identification, qualification support and pricing discussions depend on manufacturer confirmation, specifications, quantities and terms.
Detailed technical guidance, data tables, FAQs and technical references follow below.
Regulated uses. Food-contact, drinking-water, medical, pharmaceutical, electrical, fire-rated and other regulated uses need documentation and approvals for the exact product, use and market. This page is general information and confirms none of them; request the evidence in writing.
General technical information published by PAXOMER Inc. to support preliminary material evaluation. It is compiled from the sources cited on this page and has not been independently reviewed or certified by a professional engineer, laboratory or certification body. Values marked typical, illustrative or requiring confirmation are not specifications. Confirm properties, standard editions, regulatory status and suitability for your specific application with the manufacturer and, where the use is regulated or safety-related, with a qualified professional or the relevant authority.
Engineering plastic compounds combine a base polymer such as polyamide (PA6, PA66), polybutylene terephthalate (PBT), polycarbonate (PC), polyoxymethylene (POM), polyphenylene sulfide (PPS) or blends with reinforcements, fillers, flame retardants, impact modifiers, stabilisers and colourants. They are moulded or extruded into structural, electrical, automotive, appliance and industrial parts where commodity plastics lack stiffness, heat resistance, dimensional stability or flame performance.
This page is for moulders, OEM design and materials engineers and purchasing teams evaluating a compound or an alternative to an incumbent grade. It explains why conditioned properties and part-level behaviour matter more than dry datasheet values, which ISO and ASTM methods appear on data sheets, what flammability documentation means and how to plan a moulding trial. It does not state that PAXOMER stocks, manufactures or has qualified any compound, and its tables are a framework rather than confirmed values.
A. Product identity and terminology
1. What do engineering compounds do that commodity plastics cannot?
They provide higher stiffness and strength (especially with glass or mineral reinforcement), higher heat resistance, better creep and fatigue behaviour, dimensional stability, wear resistance, chemical resistance and documented flame behaviour. Manufacturer literature presents engineering and performance polymer families for such applications (S3).
2. Which polymer families and modifications are common?
| Family | Typical strengths | Points to evaluate |
|---|---|---|
| PA6, PA66 and other polyamides | Toughness, strength with glass fibre, heat ageing grades | Moisture absorption, dimensional change, hydrolysis |
| PBT and PET | Dimensional stability, electrical properties, low moisture uptake | Hydrolysis in hot humid conditions, notch sensitivity |
| Polycarbonate and blends (PC/ABS, PC/PBT) | Impact, transparency (PC), flame grades | Chemical stress cracking, notch sensitivity |
| POM (acetal) | Stiffness, low friction, dimensional stability | UV and acid resistance, bonding |
| PPS, PEEK and other high-temperature polymers | Heat and chemical resistance | Cost, processing temperatures |
Modifications include glass fibre, carbon fibre, mineral fillers, impact modifiers, flame-retardant packages (halogenated or halogen-free), heat stabilisers, UV stabilisers, lubricants and laser-marking additives.
3. Which terms appear in compound specifications?
Base polymer, glass-fibre content, dry as moulded (DAM), conditioned, tensile modulus, tensile strength, elongation, flexural modulus, notched impact, heat deflection temperature (HDT), Vicat, melt flow, shrinkage (parallel and normal), creep, weld-line strength, flammability rating, relative thermal index, comparative tracking index, colourant recognition. Glossary: melt flow rate.
B. Properties and performance
4. Why must dry and conditioned results be compared separately?
Polyamides in particular absorb moisture from the air until they reach equilibrium. Data sheets often show values dry as moulded and after conditioning. Stiffness and strength are generally lower and toughness higher in the conditioned state. Comparing one supplier's dry value with another's conditioned value produces false conclusions, and a part designed on dry data may deflect more in service.
5. Which properties should be specified, and how are they measured?
Tensile properties are reported to ISO 527 (part 2 covers moulding and extrusion plastics) (S4) or ASTM D638 (S7); flexural properties to ASTM D790 (S5) or ISO 178; notched impact to ASTM D256 (S8) or ISO 179/180; heat deflection to ASTM D648 (S6) or ISO 75; density to ASTM D792 (S9). ASTM maintains a family of plastics standards that data sheets reference (S2). State the method, specimen, condition and test speed with each value.
Engineering compound parameters to specify
Illustrative framework only. Values must be stated by the compounder for the exact grade, colour and condition.
| Property | Value or range | Unit | Test conditions | Test method | Grade or construction | Source | Verification status |
|---|---|---|---|---|---|---|---|
| Tensile modulus | stated by grade and condition | MPa | Dry or conditioned stated | ISO 527-2 or ASTM D638 | Moulded specimen | S4, S7 | Manufacturer confirmation required |
| Tensile strength | stated by grade and condition | MPa | Dry or conditioned stated | ISO 527-2 or ASTM D638 | Moulded specimen | S4, S7 | Manufacturer confirmation required |
| Flexural modulus | stated by grade | MPa | Span and speed stated | ASTM D790 | Moulded specimen | S5 | Manufacturer confirmation required |
| Notched impact | stated by grade | J/m or kJ/m² | Temperature and notch stated | ASTM D256 or ISO 179/180 | Moulded specimen | S8 | Manufacturer confirmation required |
| Heat deflection temperature | stated by grade | °C | Load stated | ASTM D648 or ISO 75 | Moulded specimen | S6 | Manufacturer confirmation required |
| Density | stated by grade | g/cm³ | Temperature stated | ASTM D792 | Moulded specimen | S9 | Manufacturer confirmation required |
| Flammability classification | per listing | rating at thickness | Thickness and colour stated | UL listing | Grade and colour | S1 | Manufacturer confirmation required |
6. Why is heat deflection temperature not a service temperature?
HDT measures the temperature at which a specimen under a defined flexural stress deflects by a set amount during heating (S6). It ranks materials but does not describe long-term behaviour under your load, time, environment and part geometry. For long-term heat exposure, ask for heat-ageing data and, where relevant, relative thermal index information from the material's listing.
7. What does a flammability rating mean?
UL describes combustion tests for plastics and maintains listings of materials tested (S1). A rating applies to a specific grade, colour and minimum thickness listed. A different colour, thickness, recycled content or compounding site may need its own listing. Ask for the listing reference and check it covers your part thickness and colour.
8. How do density and glass content affect part weight?
Reinforced compounds are denser than the base polymer. A higher glass content can allow thinner walls, but each part weighs more per unit volume, which affects cost per part and product weight. A quick estimate multiplies the part volume by the compound density; the example shows the arithmetic only.
Hypothetical part-weight comparison
Hypothetical example to show the arithmetic. Densities are illustrative values for two notional grades, not product data.
| Property | Value or range | Unit | Test conditions | Test method | Grade or construction | Source | Verification status |
|---|---|---|---|---|---|---|---|
| Part volume | 50 | cm³ | From CAD model | Input | Hypothetical part | None | Hypothetical calculation |
| Density, unreinforced grade | 1.14 | g/cm³ | Illustrative | Input | Hypothetical grade A | None | Hypothetical calculation |
| Density, glass-reinforced grade | 1.36 | g/cm³ | Illustrative | Input | Hypothetical grade B | None | Hypothetical calculation |
| Part mass, grade A | 57.0 | g | 50 × 1.14 | Arithmetic | Hypothetical | None | Hypothetical calculation |
| Part mass, grade B | 68.0 | g | 50 × 1.36 | Arithmetic | Hypothetical | None | Hypothetical calculation |
| Mass increase | 19.3 | % | (68.0 − 57.0) / 57.0 × 100 | Arithmetic | Hypothetical | None | Hypothetical calculation |
C. Manufacturing and processing
9. How are compounds produced and moulded?
Compounders melt-blend polymer with additives and reinforcements in twin-screw extruders, then pelletise. Moulders dry the pellets as required, then injection mould or extrude. Drying, melt temperature, mould temperature, injection speed, holding pressure and cooling time affect crystallinity, fibre orientation, shrinkage, warpage and surface quality.
10. Why does a moulded part behave differently from a test bar?
In a part, glass fibres align with flow, so stiffness and shrinkage differ along and across flow. Weld lines where flow fronts meet are weaker. Thick sections, ribs and bosses cool differently. Residual stress and moisture state also differ. Design reviews, mould-flow analysis and part testing are needed to confirm performance.
11. Which moulding problems are common?
| Problem | Possible causes | First checks |
|---|---|---|
| Warpage | Fibre orientation, uneven cooling, mould temperature | Gate position; cooling layout; process settings |
| Brittle parts | Insufficient drying (hydrolysis), degradation, wrong grade | Moisture before moulding; melt temperature; residence time |
| Weak weld lines | Flow-front meeting, low melt temperature, venting | Weld-line position; venting; temperatures |
| Splay and surface streaks | Moisture, volatiles | Drying records |
| Fibre visible at surface | Mould temperature, injection speed | Process settings |
| Dimensional drift in service | Moisture uptake, post-crystallisation | Conditioning; annealing; design allowances |
12. How should pellets be stored and handled?
Keep bags sealed until use; dry hygroscopic resins to the manufacturer's moisture target before moulding; avoid contamination; and follow safety data sheets for dust and processing fumes. Record lot numbers at the press.
D. Applications and qualification
13. Where are engineering compounds used?
Automotive under-hood and structural parts, electrical connectors, housings and switchgear components, appliance parts, power tools, industrial gears and bearings, fluid-handling components, building hardware and consumer products. Each application brings its own standards and approvals.
14. Which requirements depend on the application?
Electrical parts may need flammability, tracking and thermal-index documentation; automotive parts follow OEM material specifications; potable-water and food-contact parts need compliance statements; outdoor parts need UV resistance. State these early, because they can restrict which grades are acceptable.
15. How should a buyer select a candidate compound?
- Describe the part, loads, temperatures, environment and life.
- State regulatory and listing requirements.
- Ask compounders for candidate grades with dry and conditioned data, methods and listings.
- Review processing requirements against your equipment.
- Mould parts and test them against the incumbent before approving.
16. How should a moulding and part trial be organised?
Use the production mould where possible. Record drying, process settings and lot numbers. Measure dimensions after conditioning, test parts mechanically and thermally, check weld lines and assembly features, and run any application-specific tests. Compare with the incumbent under the same conditions.
17. Which documents should be requested?
Technical data sheet with methods and conditions; processing guide; flammability and electrical listings referencing grade and colour; regulatory statements for the application; lot certificates; safety data sheet; and change-notification commitment, including compounding-site changes.
E. Procurement, comparisons and decisions
18. How do engineering compounds compare with alternatives?
| Alternative | Where it may be preferred | Trade-offs to evaluate |
|---|---|---|
| Reinforced polypropylene | Lower cost, chemical resistance, lower density | Lower heat resistance and stiffness at temperature |
| Metal (die-cast aluminium, zinc, steel) | High loads and temperatures, conductivity | Weight, corrosion, secondary operations |
| Thermosets (BMC, SMC, phenolics) | High heat and dimensional stability, electrical uses | Not remeltable, cycle time |
| Rigid PVC or other sheet for fabricated parts | Low volumes, fabricated rather than moulded | See rigid PVC sheet for fabrication |
19. What determines cost per part?
Compound price per kilogram, part weight (density and wall thickness), cycle time, scrap, drying energy, mould wear from reinforcements, secondary operations, and the cost of failures. A higher-priced compound that allows thinner walls or faster cycles can reduce cost per part.
20. What should an engineering-compound RFQ include?
- Part description, drawing or volume, loads, temperatures and environment.
- Incumbent grade, if any, and the reason for change.
- Required properties with methods and condition (dry or conditioned).
- Listings and regulatory requirements, including colour and thickness.
- Processing equipment, annual volume, packaging and delivery location.
Prepare and submit these through the RFQ brief.
21. Which compounder qualification questions should be asked?
Base polymers and modifications offered; testing laboratory capability; listings held and their scope; colour matching; lot traceability; compounding locations; technical support for moulding trials; and change control. PAXOMER does not confirm any manufacturer's listings on this page.
22. Which related pages should be read next?
- Guide: Specialty polymer compounds and engineering plastics
- Related page: PCR recycled resins
- Related page: UV stabilizers, HALS and antioxidants
- Related page: Rigid PVC sheet for fabrication
Manufacturing Regions & International Supply
Countries where public company or trade sources document manufacturing relevant to Engineering Plastic Compounds, with the form of material made there and the date of the evidence. A listing is market context only. It does not indicate a PAXOMER relationship, availability or price.
- Japan: POM polymerization and engineering-plastic compounding. Product manufacturing · Company release, 2016; current status not reconfirmed · R17
- Taiwan: POM polymerization and compounding. Product manufacturing · Company release, 2016; current status not reconfirmed · R17
- Malaysia: POM and PPS production and compounding in Kuantan. Product manufacturing · Company release, 2016; current status not reconfirmed · R17
- China: the 2016 source lists POM production in mainland China. It is not listed, because later reports describe a plant suspension and replacement there.
If you are evaluating manufacturers abroad, list in your RFQ brief the destination market, the documents you require and the delivery terms.
Engineering and purchasing FAQs
Each answer is general technical information, not a specification or a quotation.
Why do two PA66 GF30 grades perform differently?
Base polymer, fibre type and sizing, stabilisers, lubricants and compounding all vary. Compare with methods and conditions stated, and test in your part.
Should I design on dry or conditioned data?
For moisture-sensitive polymers, design on the condition the part will see in service, usually conditioned, and check the extremes.
Is a UL rating valid for every colour of a grade?
Not necessarily. Listings name the grade, colours and minimum thickness covered. Check the listing for your colour and wall thickness.
Can I use HDT as my maximum service temperature?
No. HDT is an index under a defined load. Long-term service depends on load, time, environment and part design; ask for heat-ageing data.
Why must polyamide be dried before moulding?
Moisture in the melt can cause hydrolysis, splay and brittleness. Dry to the manufacturer's moisture target and record it.
Can PAXOMER help source engineering compounds?
This page does not confirm supply or listings. Send your part, requirements and incumbent grade, and PAXOMER will review whether a suitable manufacturer-development opportunity exists.
Technical References
References below were opened on the access date shown. A source supports only the statement it is cited for. Standards are cited by number and title from public catalogue entries; their full text was not read unless stated.
- S1. Combustion (Fire) Tests for Plastics. UL Solutions. www.ul.com/services/combustion-fire-tests-plastics (opens in a new tab) industry body · accessed 2026-10-28
Service page opened 2026-10-28; cited for the existence of combustion tests and material listings only. - S2. Plastics Standards. ASTM International. store.astm.org/products-services/standards-and-publications/standards/plastics-s (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue page opened 2026-10-28; cited for the existence of the ASTM plastics standards family. - S3. Performance Materials. BASF. plastics-rubber.basf.com/southamerica/en/performance_polymers (opens in a new tab) manufacturer literature · accessed 2026-10-28
Overview page opened 2026-10-28; cited for the existence of engineering and performance polymer families. Not an endorsement. - S4. ISO 527-2:2012 Plastics — Determination of tensile properties — Part 2: Test conditions for moulding and extrusion plastics. ISO, 2012. www.iso.org/standard/56046.html (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read. - S5. ASTM D790: Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials. ASTM International. store.astm.org/standards/d790 (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read. - S6. ASTM D648: Standard Test Method for Deflection Temperature of Plastics Under Flexural Load in the Edgewise Position. ASTM International. store.astm.org/standards/d648 (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read. - S7. ASTM D638: Standard Test Method for Tensile Properties of Plastics. ASTM International. store.astm.org/standards/d638 (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read. - S8. ASTM D256: Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics. ASTM International. store.astm.org/standards/d256 (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read. - S9. ASTM D792: Standard Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement. ASTM International. store.astm.org/standards/d792 (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read. - S10. Specialty polymer compounds and engineering plastics (PAXOMER guide). PAXOMER Inc., 2026-10-28. /products/specialty-polymer-compounds-engineering-plastics/ technical literature · accessed 2026-10-28
PAXOMER’s own guide; not an external source and not independently reviewed.
Regional manufacturing evidence
Company and trade publications cited in Manufacturing Regions & International Supply. Each supports only the statement it is cited for (checked 29–30 October 2026). Naming a company here does not state or imply a relationship with PAXOMER.
- R17. Polyplastics to expand plant in Malaysia (POM polymerization in Japan, Malaysia, mainland China and Taiwan). Kyodo News PR Wire / Polyplastics. kyodonewsprwire.jp/release/201601207192 (opens in a new tab) checked 2026-10-30
Evidence notes and limitations
What the information on this page does not establish. Confirm these points with the manufacturer, the current standard or the relevant authority before relying on them.
- Standards are cited by number and title; scopes and editions were not read. ISO 178, ISO 179/180 and ISO 75 are named from general practice; their catalogue pages were not opened.
- Polymer family strengths are general tendencies and not supported line by line by a recorded source.
- The densities in the part-weight example are illustrative and are not product data.
- This page has not been independently technically reviewed or certified.
Facts checked against the cited sources
- Titles of ISO 527-2:2012, ASTM D790, D648, D638, D256 and D792 were confirmed on the publishers' catalogues on 2026-10-28.
- The UL combustion tests page, the ASTM plastics standards page and the BASF performance materials page were confirmed to exist on 2026-10-28.
- The part-weight arithmetic (57.0 g, 68.0 g, 19.3 % increase) was checked.
Where this connects to the full guide
The primary technical guide behind this page is Specialty Polymer Compounds & Engineering Plastics. All its topics are indexed below.
Topics in the full guide
- Quick answer
- What does this material system do in an industrial application?
- What do the product names and technical terms mean?
- What product types and classifications are available?
- How does material composition affect performance?
- How is the material manufactured and converted?
- Which technical properties affect application performance?
- Which grades, dimensions and specifications should buyers compare?
- Where is this material used in industry?
- Which requirements depend on the intended application?
See all 40 topics in the guide
Related guides, comparisons and tools
- Specialty Polymer Compounds & Engineering Plastics Primary guide
- Specialty Polymer Additives & Processing Aids
Glossary: Polymer matrix · Glass-fibre reinforcement · Impact modification · Weld line · Heat-deflection temperature · Flame-retardant compound · Creep · Specimen conditioning
Tools: Product Finder · Manufacturer Finder
How can I submit an inquiry?
Describe your application, the specifications above and the qualification stage. The material and this page are carried into the form for you. PAXOMER replies by email; the form does not confirm stock, representation or qualification.