How to Read a Resin Datasheet for Injection Molding
Last updated: 2026-09-01 · Reading time: about 10 min
A resin datasheet is the supplier’s best-case summary of a grade: measured under the supplier’s chosen conditions, usually on test bars, usually reported as typical values.
Read it as a feasibility filter and a conversation starter — the numbers that decide your program are melt flow, drying requirements, shrinkage, heat performance and impact — and treat every value as conditional until the test conditions behind it are on the table. The datasheet tells you whether to keep talking; the DFM review is where the numbers become commitments.
Key facts
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Cavity — The hollow space inside the mold that forms the part shape. Multi-cavity molds produce multiple parts per shot. Cavity count determines production output but also mold cost and complexity. Each cavity must be balanced for uniform fill. See also related guide.
Shrinkage — The dimensional reduction from mold cavity to cooled part. Amorphous resins: 0.4–0.7% (uniform). Semi-crystalline: 1.0–2.5% (directional). Mold makers apply shrinkage factor when machining cavity. Actual shrinkage varies with wall thickness, gate location and packing pressure. See also related guide.
Why is the datasheet a starting point, not a promise?
Because of what it is for. The datasheet exists so an engineer anywhere can screen a grade in ten minutes, which means the supplier reports the values most representative of the product line — typical values, measured on their own equipment, under their own chosen conditions. That is genuinely useful: it is how the field of candidates narrows from forty grades to three. What it is not is a specification.
Shipments vary within the supplier’s stated tolerances, and the datasheet number for impact or flow can sit near the middle of a legal range your part happens to experience from the inside. Programs that treat the datasheet as a contract discover the gap at the worst time — after the tool is cut to a datasheet shrinkage the resin never quite delivered, or after an impact number that was typical became the complaint number that was real.
The professional posture is simple: narrow the field with the datasheet, then convert the decision-critical values into measured, agreed, versioned commitments during DFM — and keep the datasheet in the tool file, because the document that justified the grade is part of the tool’s history.
Which numbers actually decide feasibility?
Most of a datasheet is context. Five groups decide whether the grade fits the program, and each one comes with a question you should be in the habit of asking.
| Parameter group | What it tells you | The question to ask |
|---|---|---|
| Melt flow (MFI and conditions) | How easily the melt fills thin walls and long paths. | At which temperature and load was it measured — and does that match my machine window? |
| Drying (temperature, time, moisture target) | What the grade needs before molding. | Is this the target at the machine, and what reabsorbs after opening the bag? |
| Shrinkage (range, direction) | The tool compensation envelope. | Is this a range or a point — and is there flow-direction data for filled grades? |
| Heat (HDT, Tg/Tm, service ratings) | Where the part keeps its shape. | Under what stress and thickness was HDT measured — at 0.45 MPa or 1.8 MPa? |
| Impact (Izod, Charpy, falling dart) | How it survives knocks. | Notched or unnotched, at which thickness, at room temperature or service temperature? |
The pattern across that right-hand column is deliberate: every question is about conditions, because conditions are where datasheet comparisons go wrong. An HDT quoted at the lower stress reads dramatically higher than the same resin tested at the higher one; a notched Izod on a thin bar tells you almost nothing about a thick rib falling off a table. The grade you keep is the grade whose conditions you understand.
Typical values or tested values — which one is on your sheet?
Suppliers use both words, and the difference is a contract boundary. A typical value is the center of observed batch behavior — useful, honest, and without obligation. A tested value is data attached to a real lot, traceable to a certificate.
Where the program’s critical properties live on the datasheet as typical values, the move at DFM is to ask for what converts them into commitments: lot certificates for the incoming shipments, retention data the supplier already holds, or first-article testing on your own parts — which is why the T1 evidence list and the datasheet review are one conversation, not two meetings. Neither step is adversarial; suppliers answer these questions every day.
The failure pattern is not asking, then arguing later about whether a typical value was a promise.
What does the datasheet not cover?
Who do you talk to when the datasheet runs out?
Three desks, in this order.
First, the supplier’s technical support — not the sales desk — because they hold the data behind the datasheet: condition-specific curves, retention data, cross-references between test systems, and the guidance for your colorant and your processing window. Second, your own incoming data: lot certificates on the shipments you are actually buying, which turn the typical values on the sheet into your program’s own history.
Third, the molding floor’s evidence — the T1 report and the process sheet, which record how this grade behaved in this tool. A datasheet review that ends with a phone number instead of a dispute is the normal outcome; the datasheet is the beginning of supplier communication, not its replacement. What separates programs is whether the questions get asked before the deposit or after the first rejected shipment.
Put the questions on the review agenda by name — flow, drying, shrinkage, heat, impact, conditions, revision — and the call ends with decisions instead of impressions — which is the entire return on an hour of reading.
How do you run a datasheet review at DFM?
“A datasheet is a résumé, not a reference letter. It gets the grade an interview — the tool decides the job.”
— Arthur, Tooling Engineer at aCatMould
Frequently asked questions
Two suppliers list the same polymer family — is the datasheet the same?
Not reliably. Different producers compound differently even inside one family, and the same polymer name can carry different flow, impact and thermal packages. Compare data, not names — and if the datasheets disagree, that disagreement is information, not noise.
Why do two datasheets disagree for the same grade?
Check the test conditions first: different temperatures, loads, specimen thicknesses or conditioning produce different numbers for the same resin. If the conditions match and the values still differ, ask the supplier which revision is current — datasheets are revised, and the version matters.
Can I tool directly from the datasheet shrinkage?
Only as the starting envelope. The datasheet gives a range; the DFM review assigns compensation per feature class and records the factors on the tool drawing, and T1 reconciles the assumption against measurement. Tooling from a single datasheet number skips the only steps that catch the gap.
Are ASTM and ISO values interchangeable?
No. Specimen geometry, test speeds and calculation methods differ between the systems, so the same grade can report noticeably different tensile or impact numbers under each. Ask the supplier for cross-referenced data rather than converting by rule of thumb.
The property I need is not on the datasheet — now what?
Ask the supplier’s technical support for the deeper data they usually hold — design guides, retention data, condition-specific testing — and where it still does not exist, plan program-level evidence on your own parts. The absence of a number is a finding, not an obstacle to hide.
How do I compare grades across suppliers fairly?
On one table, under matched conditions: same test system, same specimen thickness, same temperature and load for flow, same notch and thickness for impact. Build the comparison with the conditions printed beside every value, and treat any cell missing its conditions as unread — because it is.
Does a longer datasheet mean a better-documented grade?
Not necessarily — page count is marketing, conditions are engineering. A two-page sheet with complete test conditions is worth more than a twelve-page brochure of graphs without axes you can trace. Read for the conditions and the revision date, not the word count.
Should the datasheet live in the tool file?
Yes — as a permanent attachment, not a link. Grade, supplier, revision date, and the conditions agreed at DFM belong beside the tool drawing and the T1 report, because tools outlive links, inboxes and the people who approved the program. When the tool moves, is transferred, or comes back for a modification years later, the datasheet in the file is what lets the next engineer reproduce the original decision instead of reverse-engineering it from a part that may have drifted.
A tool file without the datasheet is a drawing without dimensions — technically present, practically unusable.
Who owns the datasheet record during the program?
The DFM record does: grade, supplier, datasheet revision, and the conditions agreed for every critical value. When a shipment argues with a datasheet months later, the version number on file decides whether it is a property question or a specification question.
Key takeaways
- Datasheets screen grades; they do not specify them — typical values under the supplier’s conditions start the conversation, not end it.
- Flow, drying, shrinkage, heat and impact decide feasibility, and every value is only as good as the test conditions behind it.
- ASTM and ISO data are different systems; reconcile through the supplier, never by assumption.
- Critical properties get promoted from typical to tested — certificates, retention data or first-article evidence agreed at DFM.
- Record the grade, revision and conditions, and close the loop at T1 where the tool reports what the resin actually did.
If you have a datasheet in one hand and a drawing in the other, send us both before the deposit. You will get the five-group review against your actual geometry, the reconciliation of test conditions and systems, and the list of values worth promoting to tested evidence — from a named tooling engineer, before any steel is ordered.
Sources
MatWeb — material property database aggregating supplier datasheets
ASTM D638 — Standard Test Method for Tensile Properties of Plastics, ASTM International
ISO 20457:2018 — Plastics moulded parts: Tolerances and acceptance conditions, International Organization for Standardization
Plastics Industry Association — industry resources on plastics processing practice
Sources: Plastics Technology · Plastics Technology Online · Prospector — Resin Datasheets · MatWeb — Material Property Database