Plain-English definitions of the resin terms you’ll see on data sheets, quotes and COAs. Each term links to a deeper guide where we have one.
A · B · C · D · E · F · G · H · I · L · M · N · O · P · R · S · T · U · V · W
A
ABS — Acrylonitrile butadiene styrene, a tough, easy-molding amorphous resin. More →
Aged prime — Prime resin that is older or surplus inventory. Check manufacture date and storage. More →
Amorphous — A resin with no crystalline structure (ABS, PC, PS). Lower, more even shrinkage; usually less chemical resistance.
ASA — Acrylonitrile styrene acrylate, an outdoor-durable alternative to ABS. More →
B
Bimodal — A resin made with two molecular-weight populations, often to combine processability with toughness and stress-crack resistance (common in HDPE).
Bulk density — How much pellets weigh per unit volume; it decides how many pounds fit in a gaylord. More →
C
C4 / C6 / C8 — The comonomer in LLDPE: butene, hexene or octene. Longer comonomers give tougher film. More →
COA — Certificate of analysis: measured properties for a specific lot of resin. More →
Color concentrate (masterbatch) — Pigment at high loading in a carrier resin, let down at the press to color natural resin. More →
Compound — A base resin melt-blended with fillers, reinforcements, colorants or additives. More →
Copolymer — A polymer made from two or more monomers (for example impact copolymer PP, acetal copolymer).
Creep — Slow deformation of a part under a constant load, worse at higher temperatures. More →
D
Density — Mass per volume (g/cm³). Lower density means more parts per pound. More →
E
ESCR — Environmental stress-crack resistance: how well a resin resists cracking under stress in contact with chemicals. More →
ESD — Electrostatic discharge. ESD-safe resins are static-dissipative or conductive. More →
EVA — Ethylene-vinyl acetate; gets softer and more adhesive as vinyl acetate (VA) content rises. More →
F
FR — Flame retardant. More →
G
Gaylord — A large corrugated box on a pallet holding roughly 1,000–1,600 lb of pellets. More →
GF30 (GF15, GF33…) — Glass-fiber content by weight: GF30 means 30% glass. More →
GPPS — General-purpose (crystal) polystyrene: clear, rigid and brittle. More →
H
HALS — Hindered amine light stabilizers, additives that protect plastics from UV. More →
HDPE — High-density polyethylene. More →
HDT — Heat deflection temperature: where a test bar bends a set amount under load (0.45 or 1.8 MPa). More →
HIPS — High-impact polystyrene, toughened with rubber. More →
HLMI — High-load melt index, measured at 21.6 kg; used for very low-MI polyethylene. More →
HMW-HDPE — High molecular weight HDPE for thin strong film, pipe and large blow-molded parts. More →
Homopolymer — A polymer made from a single monomer (for example PP homopolymer). More →
Hydrolysis — Breakdown of polymer chains by water at high temperature; why PC, PET and PBT must be dried. More →
Hygroscopic — Absorbs moisture from the air (nylon, PC, PET, PBT, ABS). More →
I
Impact copolymer — Polypropylene with a rubber phase for toughness, including in the cold. More →
L
LDPE — Low-density polyethylene, with long-chain branching: easy processing and clarity. More →
LLDPE — Linear low-density polyethylene: tough film with short-chain branching. More →
LTL — Less than truckload: a shipment of a few pallets or gaylords. More →
M
MFI / MFR / MI — Melt flow index (or rate): grams of resin through a standard die in 10 minutes. Higher flows easier. More →
mLLDPE — Metallocene LLDPE: tougher, clearer film with better sealing. More →
MVR — Melt volume rate: melt flow measured by volume (cm³/10 min). More →
N
Notched Izod — A standard impact test on a notched bar; higher means tougher.
O
Off-grade / off-spec — Resin outside its producer specification. More →
P
PA (nylon) — Polyamide. PA6 and PA66 are the most common; PA11 and PA12 absorb less water. More →
PBT — Polybutylene terephthalate, a fast-molding engineering polyester. More →
PC — Polycarbonate: clear, very tough, heat resistant. More →
PCR / PIR — Post-consumer / post-industrial recycled resin. More →
PEEK — Polyetheretherketone, a top-tier high-heat, chemical-resistant resin. More →
PEI — Polyetherimide, an amorphous high-heat resin with inherent flame resistance. More →
POM (acetal) — Polyoxymethylene: stiff, low-friction, dimensionally stable. More →
PP — Polypropylene. More →
Prime — First-quality resin meeting the producer’s published spec, sold under its grade name. More →
PVDF — Polyvinylidene fluoride, a melt-processable fluoropolymer for chemical service. More →
R
Regrind — Ground-up scrap that is blended back into virgin resin. More →
S
Semi-crystalline — A resin with ordered crystalline regions (PP, PE, nylon, POM, PBT, PEEK): better chemical resistance, higher and less even shrinkage. More →
Splay — Silver streaks on molded parts, usually from moisture. More →
T
TDS — Technical data sheet: a grade’s typical properties as published by the producer.
TPE / TPU — Thermoplastic elastomer / thermoplastic polyurethane: rubber-like materials that mold like plastics. More →
U
UHMW-PE — Ultra-high molecular weight polyethylene: outstanding wear and impact; not injection moldable. More →
UL 94 — The standard flammability rating for plastics (HB, V-2, V-1, V-0, 5VA). More →
V
Vicat softening point — The temperature at which a needle penetrates the plastic a set depth; a measure of heat resistance.
W
Wide-spec — Producer-made resin outside the tight spec on one or more properties. More →
Don’t see a term? Ask us and a polymer chemist will explain it.