Last updated: 2026-09-05 · 5 min read

How to Read a Resin Datasheet — What Key Properties Matter for Injection Molding, How Do You Compare Grades, and Which Values Predict Moldability and Part Performance?

A resin datasheet (TDS) lists 15–30 properties, but only 6 matter for injection molding decisions: melt flow index (MFI), heat deflection temperature (HDT), tensile strength, impact strength, shrinkage rate and mold temperature range. MFI predicts flow behavior (high MFI = thin walls, low MFI = thick walls). HDT predicts use temperature. Shrinkage predicts ±dimensional tolerance. Reading these 6 values correctly prevents 80% of molding failures.

  • Melt Flow Index (MFI, g/10min): measures how easily the resin flows when melted. High MFI (20–40 g/10min): flows easily, fills thin walls (0.5–1.0mm), but sinks and warps more. Low MFI (5–10 g/10min): flows slowly, requires higher injection pressure, better for thick walls (2–4mm) and large parts. The MFI range determines the molding window: too high MFI at high injection speed = flash; too low MFI at low speed = short shots. Match MFI to part geometry: thin walls = high MFI, thick walls = low MFI.
  • Heat Deflection Temperature (HDT, °C at 0.46 or 1.82 MPa): temperature at which a test bar deflects 0.25mm under load. HDT at 0.46 MPa: use temperature for unsupported parts. HDT at 1.82 MPa: use temperature for load-bearing parts. Example: ABS HDT at 0.46 MPa = 95°C, at 1.82 MPa = 85°C. If the part operates at 80°C under load: ABS at 1.82 MPa (85°C) is marginal — switch to PC (HDT 130°C at 1.82 MPa). Check HDT at the load matching your application.
  • Shrinkage rate (%): the dimensional reduction from mold cavity to cooled part. Amorphous resins (ABS, PC, PS): 0.4–0.7% shrinkage (uniform, predictable). Semi-crystalline resins (PP, PA, POM): 1.0–2.5% shrinkage (non-uniform, flow-direction dependent). The shrinkage value on the datasheet is measured on a standard test bar — actual part shrinkage varies with wall thickness, gate location and packing pressure. Mold makers use the datasheet shrinkage to size the cavity, then adjust based on T1 measurements. For tight tolerance (±0.05mm): choose low-shrinkage amorphous resin.

What Six Properties on a Resin Datasheet Determine Moldability and Part Performance?

Property Unit What It Predicts Typical Range (ABS)
Melt Flow Index (MFI) g/10min Flow ease, thin-wall fillability 10–25
HDT at 0.46 MPa °C Max use temperature (unloaded) 95–105
HDT at 1.82 MPa °C Max use temperature (loaded) 85–95
Tensile strength MPa Resistance to pulling forces 40–50
Impact strength (Izod) kJ/m² Resistance to sudden impact 15–25
Shrinkage rate % Dimensional change from mold to part 0.4–0.7

The other properties on the datasheet (density, flexural modulus, elongation at break, dielectric strength, flammability rating) are useful for specific applications but do not determine whether the resin will mold successfully. Focus on the 6 key properties for moldability and general part performance. The remaining properties are secondary checks for regulatory or application-specific requirements.

Typical value vs. guaranteed value — datasheet properties are reported as either typical (average of recent batches, may vary ±10–15%) or guaranteed (minimum value every shipment meets). For critical design properties (impact, HDT): always use the guaranteed value. If typical impact is 20 kJ/m² but guaranteed minimum is 15 kJ/m²: the design must work at 15. The tolerance guide shows how shrinkage variation affects dimensional accuracy.

What Three Steps Ensure You Select the Right Resin Grade from the Datasheet?

  1. Match MFI to part geometry — thin walls need high MFI, thick walls need low MFI. Wall below 1.0mm: MFI above 20 g/10min (fills thin sections). Wall 1.5–3.0mm: MFI 10–20 (balanced flow and packing). Wall above 3.0mm: MFI 5–12 (slow flow prevents jetting and air traps). MFI also affects cycle time: high MFI cools faster but may need longer packing to prevent sink. Request 2–3 grades with different MFI from the supplier and run flow simulations to confirm fill.
  2. Check HDT at the correct load — 0.46 MPa for cosmetic parts, 1.82 MPa for structural. Many datasheets report HDT at 0.46 MPa only (the higher number). If the part carries load at elevated temperature: use HDT at 1.82 MPa. Example: car interior clip at 85°C. ABS HDT at 0.46 MPa = 95°C (looks OK). ABS HDT at 1.82 MPa = 85°C (marginal — clip creeps). Switch to PC/ABS: HDT at 1.82 MPa = 110°C (safe). Always check HDT at the load matching the application.
  3. Use shrinkage rate to estimate dimensional tolerance — high shrinkage means looser tolerance. Amorphous resins (ABS, PC, PS): shrinkage 0.4–0.7%, tolerance ±0.10–0.15mm achievable. Semi-crystalline resins (PP, PA, POM): shrinkage 1.0–2.5%, tolerance ±0.15–0.30mm. Glass-filled resins: shrinkage 0.2–0.8% in flow direction (lower than unfilled), but 0.8–1.5% transverse to flow (anisotropic). For tight tolerance (±0.05mm): choose amorphous resin with low shrinkage (PC at 0.5–0.7%). For loose tolerance (±0.25mm): semi-crystalline is acceptable (PP at 1.5–2.0%).

Anisotropic shrinkage — shrinkage that differs by direction. Semi-crystalline and glass-filled resins shrink less in the flow direction and more transverse to flow. For GF-PA: 0.2% flow, 1.0% transverse. This causes warpage if the part has asymmetric walls. The mold maker compensates by adjusting gate location and packing pressure. The fiber orientation warpage guide covers how glass fiber alignment amplifies anisotropic shrinkage.

Resin datasheet: 6 key properties determine moldability. MFI: flow ease (thin wall = high MFI). HDT: use temperature (check at correct load). Shrinkage: dimensional tolerance (amorphous 0.4–0.7%, semi-crystalline 1.0–2.5%). Match MFI to geometry, HDT to load, shrinkage to tolerance.

  • MFI matched to wall thickness — thin wall (<1mm) = high MFI; thick (>3mm) = low MFI.
  • HDT checked at correct load — 0.46 MPa unloaded; 1.82 MPa load-bearing.
  • Shrinkage rate vs. tolerance requirement — amorphous 0.4–0.7% for tight tolerance.
  • Guaranteed values used for design — not typical values (may vary ±15%).
  • Test conditions consistent — ASTM vs. ISO values not directly comparable.

Frequently Asked Questions

How do I compare two resin grades from different suppliers on the same datasheet?

Compare the 6 key properties at the same test conditions (ASTM D638 tensile, ASTM D256 impact, ASTM D648 HDT). Some suppliers test at ISO conditions (different specimen size): values are not directly comparable. If one supplier reports MFI at 220°C/1 kg and another at 230°C/1 kg: values differ 5–15% due to temperature. Request both suppliers to test at the same conditions, or use flow simulation data for practical comparison. Datasheet comparison is a starting point — T1 sampling confirms actual performance.

What does “typical value” vs. “guaranteed value” on a datasheet mean?

“Typical value” is the average from recent batches — actual shipment may vary ±10–15%. “Guaranteed value” (or “minimum value”) is what the supplier guarantees — every shipment meets or exceeds this. For critical properties (impact, HDT): use the guaranteed value for design, not the typical. If the datasheet shows only typical values: request the guaranteed specification. The difference matters: typical impact 20 kJ/m² may have guaranteed minimum 15 kJ/m² — the design must work at 15, not 20.

Can I use the shrinkage rate on the datasheet to set the mold dimensions?

Datasheet shrinkage is a starting point — measured on a standard test bar (3.2mm thick, 127mm long) under controlled conditions. Actual shrinkage varies with: wall thickness (thicker shrinks more), gate location (flow direction shrinks less than transverse), and packing pressure (higher packing reduces shrinkage). The mold maker uses datasheet value for initial cavity dimensions, then adjusts based on T1 measurements. Expect ±0.05–0.10mm deviation from predicted. Plan for one mold trial and adjustment before cavity is finalized.

Key Takeaways

  • 6 key properties: MFI, HDT, tensile, impact, shrinkage, mold temp.
  • MFI: thin walls = high MFI (20+). Thick walls = low MFI (5–12).
  • HDT: check at correct load (0.46 or 1.82 MPa).
  • Shrinkage: amorphous 0.4–0.7% (tight tolerance). Semi-crystalline 1–2.5%.

Send the part drawing, application requirements and target resin type — the review reads the resin datasheet, identifies the optimal grade (MFI, HDT, shrinkage match), and specifies the processing window for consistent part quality.

Sources: Plastics Technology — How to Read a Resin Datasheet for Injection Molding · Plastics Technology Online — Understanding Material Property Data Sheets · Society of Plastics Engineers (SPE) — Resin Selection and Datasheet Interpretation · Prospector — Resin Datasheet Database and Property Comparison · ThomasNet — Injection Molding Resin Selection Guide

— Arthur, Tooling Engineer at aCatMould