Glass transition temperature Tg
Definition: Temperature range in which amorphous polymers transition from glassy (hard-elastic) to rubbery (soft-elastic) state. For semi-crystalline polymers, Tg refers to the amorphous fraction only.
Standard: ISO 11357-2 (DSC) or ISO 6721 (DMA). DSC measures the inflection point in heat flow; DMA the maximum tan delta.
Typical values: PC ≈ 145 °C · PET ≈ 75 °C · PS ≈ 100 °C · PVC ≈ 80 °C · PMMA ≈ 105 °C · ABS ≈ 105 °C · PA 6 ≈ 50 °C (dry).
Significance: Above Tg, modulus of amorphous polymers drops by 2–3 orders of magnitude. Critical for high-temperature applications. Related: HDT/A (below).
Heat deflection temperature HDT/A
Definition: Temperature at which a test specimen reaches defined deflection under bending load. HDT/A: 1.8 MPa (structural parts). HDT/B: 0.45 MPa (less stringent).
Standard: ISO 75-2 (EU); ASTM D648 (US).
Typical values (HDT/A): PA 66 unfilled ≈ 80 °C · PA 66-GF30 ≈ 240 °C · PC ≈ 130 °C · PEEK unfilled ≈ 160 °C · PEEK-GF30 > 300 °C · PP homopolymer ≈ 60 °C.
Significance: Standard material-selection criterion for thermally loaded parts. Rule of thumb: continuous use temperature ≈ HDT/A minus 30–50 °C.
Melt flow rate MFR
Definition: Mass flow rate (g/10 min) through standardized die at defined temperature and load. Indicator for melt viscosity and indirectly for molar mass.
Standard: ISO 1133-1 (gravimetric method A); ASTM D1238 (US).
Typical values: PE-HD blow-molding 0.3 g/10min (190 °C/2.16 kg) · PP injection 12–25 g/10min (230 °C/2.16 kg) · PA 66 injection 25–45 g/10min (275 °C/0.325 kg).
Significance: Low MFR = high molar mass = better mechanics, harder to process. High MFR = easy processing, thin walls possible, lower strength. Related: MVR (melt volume rate, cm³/10min).
Intrinsic viscosity IV
Definition: Intrinsic viscosity number in dl/g — directly correlated with molar mass. Decisive characteristic for PET.
Standard: ISO 1628-5 (solution viscometry in phenol/dichlorobenzene or phenol/TCE).
Typical values (PET): Film grade 0.60–0.68 dl/g · Bottle grade 0.80–0.85 dl/g · Tire-cord grade 0.95–1.05 dl/g.
Significance: Higher IV = higher melt strength for stretch-blow processing. In recycling (rPET), IV drops by 0.02–0.05 dl/g per cycle — solid-state postcondensation (SSP) raises it again. Critical for PPWR recyclate acceptance.
K value (Fikentscher) — PVC molar mass
Definition: Fikentscher's K constant — PVC molar-mass indicator derived from relative viscosity of 0.5% solution in cyclohexanone.
Standard: DIN 53726 / ISO 1628-2.
Typical values: K=57–60 (films, low molar mass) · K=64–66 (pipes) · K=68–72 (hard PVC for pressure applications) · K=80 (specialty PVC for records / cable insulation).
Significance: High K value = higher impact strength but harder to process. PVC processors select K value by application. Not to be confused with K-factor (thermal conductivity) in construction!
Shore hardness A and D
Definition: Indentation hardness. Shore A for elastomers and soft plastics (truncated-cone indenter), Shore D for hard plastics (conical-pointed indenter). Scale 0–100, higher = harder.
Standard: ISO 868 or DIN 53505; ASTM D2240.
Typical values: EPDM seal Shore A 60–70 · TPU Shore A 80–95 · PE-LD Shore D ≈ 45–60 · PVC-U Shore D ≈ 85 · POM Shore D ≈ 80.
Significance: Standard selection criterion for seals, grips, sporting goods. Overlap between Shore A and D: approx. Shore A 95 ≈ Shore D 45.
Density ρ
Definition: Mass per volume in g/cm³ at 23 °C after conditioning.
Standard: ISO 1183-1 (buoyancy in liquid or pycnometer).
Typical values: PP 0.90–0.91 (lightest technical plastic) · PE-HD 0.94–0.97 · PA 6 1.12–1.15 · PC 1.20 · PVC-U 1.38–1.41 · PTFE 2.15–2.20 (highest standard density).
Significance: Volume calculation for parts (material usage × density × price). Critical for recycling-sort sink/float method: PP/PE float in water, others sink.
Young's modulus E
Definition: Stiffness. Stress over elastic strain in linear range, MPa.
Standard: ISO 527-1/-2 (tensile test).
Typical values: LDPE ≈ 200 MPa · HDPE ≈ 1100 MPa · PP ≈ 1500 MPa · ABS ≈ 2300 MPa · PA 66 dry ≈ 3000 MPa · PA 66-GF30 ≈ 8500 MPa · PEEK-GF30 ≈ 10000 MPa.
Significance: Stiffness is the most important selection criterion for structural parts. Glass-fiber reinforcement typically multiplies E by 3–5×. Note: PA loses up to 60% of dry E modulus on water absorption.
Charpy notched impact aN
Definition: Impact energy per fractured net cross-section, kJ/m². Measures brittle-fracture tendency under dynamic load.
Standard: ISO 179-1 (notched variant eA notched).
Typical values: PS brittle 2 kJ/m² · PMMA 2–3 · PC very tough 70–80 (unfilled!) · PA 66-GF30 8–12 · POM 6–10 · PEEK 5–8 · ABS 15–25 (tough).
Significance: Selection criterion for shock-loaded applications (helmets, housings, protective equipment). PC and impact-modified polyamides are standard. PMMA and PS are inherently brittle — avoid for shock-loaded parts.
Processing shrinkage S
Definition: Linear dimension reduction of an injection-molded part vs the mold dimension, in %.
Standard: ISO 294-4 (linear processing shrinkage) and ISO 2577 (thermosets).
Typical values: Amorphous polymers (PS, ABS, PC, PMMA) 0.4–0.8% isotropic · semi-crystalline parallel to flow direction 1.0–2.5% (PE-HD, PP, PA 6, POM) · semi-crystalline transverse 1.5–3.0% (anisotropy!).
Significance: Mold enlargement must compensate for shrinkage. In GF-reinforced semi-crystallines, shrinkage drops sharply in fiber direction (fiber orientation). Important: factor in post-shrinkage over hours/days.
Water absorption ψ (Psi)
Definition: Mass increase from water absorption, % after 24 h or saturation in standard climate 23 °C / 50% RH.
Standard: ISO 62 (method 1 = 24h immersion, method 2 = saturation 23 °C).
Typical values: PP/PE < 0.1% (practically non-hygroscopic) · PC ≈ 0.3% · ABS ≈ 0.3% · POM ≈ 0.8% · PA 6 saturated 9% · PA 66 saturated 8%.
Significance: Hygroscopic polymers (PA, PBT, PC) must be dried before injection (residual moisture < 0.15%). Water absorption significantly changes E modulus, impact strength, and dimensional stability of PA — conditioning (equilibrium moisture) must be considered in design.
Mooney viscosity ML(1+4)
Definition: Viscosity measure for unvulcanized rubbers and elastomer compounds. Measured at 100 °C with large rotor disc, 1 min preheat + 4 min measurement time.
Standard: ISO 289-1 (method A) or ASTM D1646.
Typical values: Natural rubber 60–95 ML(1+4) · EPDM 30–80 (depending on diene content and molar mass) · NBR 45–75 · silicone 30–60.
Significance: Key incoming-inspection test for rubber processors. Higher values = higher molar mass = better mechanical properties of vulcanizate, but harder to process. Mooney-scorch value (additional test) measures onset of pre-vulcanization.
Related resources
For detailed property data per polymer see the Materials overview. For standards detail pages see ISO Standards overview.
Methodologically grounded market data on polymer prices via our Polymer Price live ticker with daily updates and open methodology documentation.