The short answer
A technical data sheet (TDS) lists typical properties of a grade, measured on standard test bars by ASTM or ISO methods. Read the test method, units and conditions next to every number before comparing grades, and use the COA to see what was measured on your actual lot.
Data sheets look precise, but two sheets for similar resins can be hard to compare if they use different methods, units or test conditions. This guide explains what each common property means, what to watch for, and how to compare grades when you are looking for an equivalent.
The properties that matter
| Property | What it measures | What to watch for |
|---|---|---|
| Melt flow rate (MFR / MFI) | How easily the melt flows at a set temperature and load | Higher flows easier and fills thin walls; lower is usually tougher. Compare only at the same temperature and load |
| Density / specific gravity | Mass per volume | Drives part weight and cost per part; filled grades are heavier |
| Tensile strength and elongation | How much pull the material takes and how far it stretches | Elongation hints at ductility; glass-filled grades usually stretch only a few percent |
| Flexural modulus | Stiffness in bending | The best single number for how rigid a part will feel |
| Notched Izod or Charpy impact | Toughness with a notch, at a set temperature | Watch the units and the method; cold-temperature values matter for outdoor parts |
| Heat deflection temperature (HDT) | Temperature where a test bar bends under load | Check the load: 0.45 MPa and 1.8 MPa give very different numbers |
| Melting point or Vicat | When the material softens or melts | Sets the processing window; gives a rough upper bound on heat resistance |
| Mold shrinkage | How much the part shrinks from the mold size | Filled grades shrink differently along and across flow |
| Flammability (UL 94) | Burn behavior at a stated thickness | The rating applies only at the thickness listed, and only to that exact grade |
| Water absorption | Moisture picked up in 24 h or at saturation | High values (nylon) mean properties and dimensions change in use |
ASTM vs. ISO
North American data sheets often use ASTM methods; European and many global producers use ISO. The methods use different specimen shapes, speeds and conditions, so the same resin gives different values. Compare ASTM to ASTM and ISO to ISO whenever you can. Our unit converter handles the unit math, but it cannot turn an ASTM result into an ISO one.
Conditions change the numbers
- Dry vs. conditioned. Nylon data is often “dry as molded”; conditioned values at 50% relative humidity are closer to real use.
- Temperature. Impact strength at −30°C can be a fraction of the room-temperature value.
- Thickness. Flame ratings and some electrical values apply only at the thickness listed.
- Load. Heat deflection at 0.45 MPa is always higher than at 1.8 MPa.
Comparing two grades for an equivalent
- Match the base polymer and filler. Same polymer family, same filler type and percentage.
- Match melt flow at the same test conditions, within a reasonable band.
- Check the critical properties for your part: stiffness, impact, heat, flame rating.
- Check approvals. UL, automotive and food-contact approvals belong to the specific grade, not the family.
- Run a trial and measure first parts before switching production.
See also melt flow index explained, finding an equivalent for a discontinued grade and the resin comparison tool.
How we help
Send the data sheet for the grade you run now, from any producer, and a polymer chemist will match it or find a qualified equivalent and price it. Every lot ships with a COA, tested to ASTM or ISO methods. We aim to send your quote within one to three business days.
Common questions
What is the difference between a TDS and a COA?
A technical data sheet (TDS) gives typical properties for a grade, measured on standard test bars. A certificate of analysis (COA) reports measured results for one specific lot. The TDS tells you what the grade is designed to be; the COA tells you what you actually received.
Can I compare ASTM and ISO data sheet values?
Only roughly. ASTM and ISO methods use different specimens and conditions, so the same resin gives different numbers. Impact strength is the clearest case: ASTM Izod in J/m and ISO Izod in kJ/m² cannot be converted into each other.
What does 'dry as molded' mean on a nylon data sheet?
The test bars were tested right after molding, before they absorbed moisture. Nylon in real use absorbs water and loses stiffness, so look for conditioned values (often at 50% relative humidity) to see how the part will behave.
Is a typical value a guaranteed value?
No. Typical values are averages, not specifications. Lot-to-lot results vary within the producer's limits. If a property is critical, ask which properties are reported on the COA or agree a specification with the supplier.
Which data sheet values matter most for an equivalent grade?
Base polymer, filler type and percentage, melt flow (or viscosity), heat deflection, flexural modulus, impact strength, flame rating and any approvals. Match those first, then check color, additives and processing notes.
Send the data sheet you need matched
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province