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How to Read a Plastic Datasheet: Key Properties Every Engineer Must Check
Understanding Datasheet Structure
Most engineering plastic datasheets follow a similar structure:
1. Header: Material name, grade, manufacturer
2. Mechanical properties: Tensile, flexural, impact, hardness
3. Thermal properties: Melting point, glass transition, HDT
4. Electrical properties: Dielectric strength, volume resistivity
5. Physical properties: Density, water absorption, shrinkage
6. Test standards: ASTM, ISO, or IEC methods used
Understanding which properties matter for your application is the key to effective datasheet analysis.
Critical Mechanical Properties
Tensile Strength
Measures the maximum stress a material can withstand before breaking. For load-bearing applications, this is often the primary selection criterion.
· PEEK: 90-100 MPa (unfilled), 150-170 MPa (30% GF)
· POM: 60-70 MPa
· PPS GF40: 130-150 MPa
· PEI: 85-100 MPa
· PA66: 70-85 MPa (dry)
Flexural Modulus
Indicates stiffness — higher values mean more rigid material. For structural parts requiring dimensional stability under load, prioritize high flexural modulus.
Impact Strength (Notched Izod)
Measures toughness and resistance to sudden impact. Critical for applications subject to mechanical shock. POM and PA66 offer excellent impact resistance.
Hardness (Shore D / Rockwell M)
Indicates surface hardness. Higher hardness means better wear resistance but may indicate brittleness. See our material comparison guides for specific values.
Critical Thermal Properties
Melting Point (Tm)
The temperature at which the crystalline structure breaks down. Amorphous materials (like PEI) don’t have a true melting point — they have a glass transition temperature instead.
Material | Melting Point (°C) |
PEEK | 343 |
PPS | 280 |
POM | 165-175 |
PA66 | 260 |
PEI | 217 (Tg, amorphous) |
Heat Deflection Temperature (HDT)
The temperature at which a material deflects under a specified load (typically 0.45 MPa or 1.8 MPa). HDT is more practically relevant than melting point for application engineering.
Glass Transition Temperature (Tg)
The temperature above which an amorphous polymer becomes rubbery. For PEEK, Tg is 143°C — above this, mechanical properties gradually decrease even though the melting point is 343°C.
Critical Physical Properties
Density
Affects weight calculations and cost-per-part. Filled grades (e.g., PPS GF40) have higher densities than unfilled grades.
Water Absorption
Critical for dimensional stability in humid environments. POM and PPS absorb minimal moisture (<0.1%), while PA66 absorbs 2.5-3.5% — affecting dimensions and mechanical properties.
Mold Shrinkage
Important for injection-molded parts but less relevant for stock shape machining. Low shrinkage (PEEK, POM) means better dimensional accuracy.
Electrical Properties
Surface Resistivity
Critical for ESD material selection. Standard plastics have surface resistivity of 10^12-10^16 ohms. ESD grades are engineered to 10^6-10^9 ohms.
Dielectric Strength
Important for electrical insulation applications. PEEK and PEI offer excellent dielectric properties.
Red Flags in Datasheets
Watch for these warning signs:
1. Missing test standards: Properties without ASTM/ISO references may not be comparable
2. Generic ranges: Very wide property ranges suggest inconsistent material quality
3. No test conditions: Properties change with temperature, humidity, and testing speed
4. No grade identification: A datasheet without a specific grade number is incomplete
5. Outdated revision: Ensure the datasheet is current — material formulations change
Practical Tips for Datasheet Analysis
1. Compare apples to apples: Ensure all materials you’re comparing use the same test standards
2. Check at application temperature: Properties at room temperature differ from those at elevated temperatures
3. Consider long-term properties: Creep, fatigue, and aging aren’t always on datasheets but may be critical
4. Request additional data: Manufacturers can provide creep curves, fatigue data, and chemical resistance charts on request. See our PEEK chemical resistance guide for an example.
FAQ
Q1: What are the most important properties to check on a plastic datasheet?
Key properties include tensile strength, flexural modulus, impact strength, heat deflection temperature, density, water absorption, and surface resistivity.
Q2: What is the difference between melting point and HDT?
Melting point is where crystalline structure breaks down; HDT is where the material deflects under load. HDT is more practically relevant for application engineering.
Q3: Why is water absorption important?
Water absorption affects dimensional stability and mechanical properties. PA66 absorbs 2.5-3.5% moisture, while POM and PPS absorb less than 0.1%.
Ready to source quality engineering plastics? Contact NAGOMER today for a free quote, or browse our PEEK sheets, POM rods, and ESD materials.
NAGOMER — Professional Engineering Plastics Solutions
www.nagomer.com | info@nagomer.com