The short answer
First try to buy the same grade from another source; that is the same product. If you need a qualified equivalent, match the base polymer, filler type and level, melt flow, additive package, color and the properties and listings your part depends on, then trial it in your mold. A grade that matches on paper still needs a trial, and approved parts need customer approval before production.
Buyers look for equivalents when a grade is short, on allocation, discontinued, or simply when they want a second source. The work is the same each time: find a close match, then prove it in the part.
Same grade vs. qualified equivalent
The same grade, bought from a different distributor, is the identical product from the same producer. For most parts it is not a material change while it stays in the producer’s sealed packaging, though some automotive and medical customers still want notice of a new source. A qualified equivalent is a different product, from another producer or a different line, chosen because its properties match. It is a material change, even when the numbers line up. See why you need a second source and replacing a discontinued grade.
What to match
| Property to match | Why it matters | Typical tolerance to look for |
|---|---|---|
| Base polymer | Defines chemistry, chemical resistance and processing | Same family and type (for example PA66, not PA6; copolymer vs. homopolymer) |
| Filler type and % | Drives stiffness, strength, shrinkage and warp | Same filler type; same nominal level (for example 30% glass, not 25% or 33%) |
| Melt flow or viscosity | Affects fill, packing and cycle | Compare at the same temperature and load; look for roughly ±20–30% or a similar viscosity class |
| Additives | Heat stabilizer, UV, lubricant, impact modifier or FR change service life and processing | Same package type; ask if the data sheet is silent |
| Mechanical properties | Tensile, flex modulus and impact set part performance | Within about 10–15% on the values that matter for the part |
| Heat deflection (HDT) | Short-term heat resistance under load | Same load (0.45 or 1.8 MPa); within about 5–10°C / 9–18°F |
| Mold shrinkage | Sets part dimensions in an existing tool | Same range, along and across flow; small differences can matter for tight tolerances |
| Density | Part weight and parts per pound | Within about 0.02 g/cm³ for filled grades; much closer for polyethylene, where density sets stiffness |
| Color | Appearance and, for rated grades, the listing | Same color system; custom colors need a new match |
| Regulatory listings | UL 94, RTI, FDA, NSF, automotive specs | Same or better rating at the same or thinner thickness and in your color |
Typical starting points for screening candidates, not acceptance limits. Values vary by grade, and your part's requirements and your customer's specification decide what is acceptable.
How to use a data sheet to match
- Decode the callout. A drawing code such as PA66-GF30 gives the family and filler. The material code decoder explains the abbreviations.
- Read the method next to every number. ASTM and ISO results are not directly comparable, and test conditions (dry vs. conditioned, 0.45 vs. 1.8 MPa) move the values. See how to read a resin data sheet.
- Screen on the basics. Polymer, filler, melt flow and additives first. A grade that misses here is not an equivalent, whatever the other numbers say.
- Compare the properties your part depends on. A snap fit cares about elongation and impact; a bracket under load cares about modulus and creep; a hot part cares about HDT and RTI.
- Check listings last, but strictly. A UL 94 rating belongs to a specific grade, at a stated thickness and color. The equivalent needs its own listing that covers your part. See flame-rated parts.
The resin comparison tool shows typical family values side by side. If you would rather hand it off, send us the data sheet and a polymer chemist will look for the same grade first, then an equivalent.
Why "equivalent on paper" is not "approved"
- Customer and OEM approval. If the drawing names a grade or the customer approved one, a change needs their sign-off.
- Automotive PPAP. A material or source change on a production automotive part normally means notifying the customer and, unless the customer waives it, submitting a new PPAP before shipping.
- Tooling and shrinkage. The tool was cut for the original grade's shrinkage. Two glass-filled grades with the same glass content can shrink and warp differently because of fiber length, sizing and the base resin.
- Data sheets are typical values. They describe standard test bars, not your part, and they do not cover everything (weld-line strength, long-term creep, chemical resistance to your fluids).
- Regulatory status is grade-specific. FDA compliance, UL listings and automotive material specifications attach to a named grade, not to a family.
How to run a trial
- Get a sample with its COA, enough for a meaningful run in the production mold.
- Dry and process it per its own data sheet, starting from your current process and recording any changes.
- Measure first-article parts after they have fully cooled and conditioned, against the drawing and against parts from the original grade.
- Check function: assembly, snap fits, torque, drop or impact, heat or chemical exposure, whatever the part sees in service.
- Document the result and submit it for customer approval where required, before production orders.
What to send us for a quote
- The grade you run now, or its data sheet
- Color, and any listings the part needs (UL, FDA, automotive spec)
- Whether you need the same grade only, or will consider an equivalent
- Quantity per order, yearly usage and ship-to city
Any change of grade or source is agreed with you in writing first. We aim to send your quote within one to three business days.
Common questions
What is an equivalent resin grade?
A grade from a different producer, or a different grade from the same producer, whose data sheet properties closely match the grade you run. It is a different product, so it needs a trial and, for approved parts, customer approval before use.
Is the same grade from another distributor an equivalent?
No, it is the same product. Buying the identical grade from another seller is normally not a material change. An equivalent from another producer is a material change even when the properties match.
What properties should match on an equivalent grade?
Start with the base polymer, filler type and percentage, and melt flow at the same test conditions. Then check additives (heat stabilizer, UV, flame retardant), color, key mechanical and thermal values, mold shrinkage, and any regulatory listings such as UL 94, FDA or automotive specifications.
Can I compare ASTM and ISO data sheet values?
Not directly. The methods use different specimens and test conditions, so the same resin gives different numbers. Compare ASTM to ASTM and ISO to ISO wherever you can.
Does an equivalent grade need PPAP for automotive parts?
Usually yes. A change of material or source on a production automotive part normally requires notifying the customer and, unless the customer waives it, submitting a new PPAP before shipping parts made from it.
How do I trial an equivalent grade?
Get a sample with its COA, run it in the production mold with the current process as a starting point, then check first-article dimensions, appearance and function against the drawing and the parts made from the original grade.
Tell us the grade you need to match
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