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Injection Molding Material Comparison — Property Table

RCRay Chan·2026-08-18·20 min read
Table of Contents

Why material choice drives cost and performance

The resin you pick decides cycle time, tool wear, post-processing and end-use limits. Below is a working comparison of the plastics we mold most often for buyers weighing spec against budget — drawn from published material data and programs we have run.

Resin selection is the first decision in any injection molding program, and it ripples through everything that follows. A semi-crystalline resin such as PP or POM shrinks two to three times more than an amorphous resin such as PC or PMMA, which changes the draft angles, the gate plan and the tolerance the tool can be quoted against. A moisture-sensitive resin such as PA66 forces a drying step into every shift, which changes the cycle schedule. A flame-retardant grade changes the additive package, which can shift color, flow and price. In other words: the material table below is not a list of interchangeable rows — it is a map of the trade-offs that determine whether a part ships on time, holds dimension and meets its regulatory class.

We are a manufacturer ourselves — Dongguan-based, with injection molding, mold making, overmolding, insert molding and low-volume production in-house — so the numbers below are the ones we quote against, and the program references come from tools we have actually built and run.

The Snapshot

  • Service temperature spans the range: ABS ~80–100 °C to PEEK 250–260 °C (260 °C continuous, ~300 °C short-term per FirstMold), with PPS filling the 200–240 °C high-heat band.
  • Shrinkage drives DFM: amorphous resins (PC, PMMA, PS) shrink 0.2–0.7%; semi-crystalline (PP, PE, POM, PA) shrink 1.0–3.0% and need more draft.
  • Flame class varies by grade: enclosures near electronics often require UL94 V-0 (flame-out ≤10 s, no drips); PPS / PEEK are inherently V-0.
  • Cost spans ~50×: PP at $1–2.5/kg and 0.90 g/cm³ is the value floor; PEEK at $50–100/kg is the performance ceiling — moving from one to the other can cut resin cost 5–10× while keeping 200 °C+ service.
  • Real programs prove the table: a VR remote in PC+ABS held ±0.04 mm at 800K units/year; a PEEK-class MRI balun ran 15,000+ units/year in PEI.

Table of Contents

  1. Full property comparison table
  2. Shrinkage and resin class for DFM
  3. Processing windows: melt, mold and drying
  4. Heat, flame and moisture handling
  5. Decision shortcut by function
  6. Materials by industry
  7. Real programs behind the table
  8. Combining materials: overmolding and inserts
  9. The cost map by resin family
  10. Regulatory and sustainability reading
  11. Common material-selection mistakes
  12. Frequently Asked Questions
  13. Sources
  14. Related resources

Full property comparison table

Density, service temperature, tensile strength, mold shrinkage and processing temperatures below are typical published datasheet ranges — exact values vary by grade, filler loading and test standard, so treat them as selection bands, not certification values. UL94 entries are grade-dependent: flame-retardant (FR) grades of normally HB-rated resins exist, and they cost more and flow differently.

Material Density (g/cm³) Service temp (°C) Tensile (MPa) Mold shrink (%) Melt temp (°C) Mold temp (°C) UL94 (typical, grade-dep.) Typical use
ABS 1.05 80–100 40–50 0.4–0.7 200–260 40–80 V-2 to V-0 (FR grades) Housings, brackets
PP (Polypropylene) 0.90 100–120 25–35 1.0–2.5 200–280 20–60 HB (V-0 FR grades) Hinges, living parts
PE (Polyethylene) 0.94 80–100 20–30 1.5–3.0 180–280 20–60 HB Containers, liners
PC (Polycarbonate) 1.20 115–130 60–70 0.5–0.7 280–320 80–120 V-2 (V-0 FR grades) Transparent, impact
POM (Acetal) 1.41 90–120 60–70 1.8–3.0 180–230 80–120 HB (V-0 grades exist) Gears, precision wear
PA (Nylon) 1.14 80–120 70–90 1.0–2.0 260–300 60–100 V-2 (V-0 FR grades) Bearings, structural
PEEK 1.32 250–260 90–100 1.1–1.4 350–400 160–200 V-0 Aerospace, medical
TPU 1.10–1.20 80–120 30–50 0.8–1.8 190–220 20–60 HB–V-0 by grade Soft-touch, gaskets
PMMA (Acrylic) 1.18 80–100 50–70 0.2–0.6 220–260 60–90 HB Optics, light pipes
PPS 1.35 200–240 70–90 0.2–0.6 300–340 120–160 V-0 Chemical, electrical
PVC 1.38 60–80 40–50 0.2–0.5 180–210 20–60 V-0 (rigid) Profiles, enclosures
PS (Polystyrene) 1.05 70–90 40–55 0.4–0.7 200–260 20–60 HB Disposable, rigid

Two reading notes. First, density matters for cost: PP at 0.90 g/cm³ buys more parts per kilogram than PVC at 1.38 g/cm³ — the same 1 kg of resin makes about 50% more PP parts by volume. Second, service temperature is a floor for the application, not a ceiling for processing: a PEEK part rated 250–260 °C runs through a melt at 350–400 °C.

Shrinkage and resin class for DFM

Shrinkage above 2% (PP, PE, POM) demands more generous draft and tighter gate control. Amorphous resins (PC, PMMA, PS) hold tighter tolerances than semi-crystalline ones (PP, PE, POM). For humid environments, absorbent resins (PA, PBT) need drying before molding or you get splay.

The practical scale of the difference shows up when you change resin on an existing tool. Protolabs publishes shrink rates of 0.003 in/in (0.076 mm/mm) for ABS versus 0.018 in/in (0.457 mm/mm) for PP — switching a tool built for ABS to PP yields parts roughly 0.015 in/in (0.38 mm/mm) smaller (https://www.protolabs.com/resources/blog/understanding-injection-molding-tolerances/). That is the fastest way to understand why resin class, not tolerance callout, sets what a mold can deliver.

A PA6-GF30 HV busbar program at 250,000+ units/year required pre-conditioning because moisture shifted dimensions by 0.2–0.5% — shrinkage and moisture are the two variables that break a tolerance if ignored.

Glass reinforcement is the other lever. FirstMold publishes a glass-filled PP ladder (GF10/20/30/40) with tensile strength climbing from ~45 to ~95 MPa, HDT from ~145 to ~165 °C, and mold shrinkage dropping from ~0.8% to ~0.5% (https://firstmold.com/pp-injection-molding/):

PP grade Tensile (MPa) HDT (°C) Mold shrink (%)
PP-GF10 ~45 ~145 ~0.8
PP-GF20 ~60 ~152 ~0.7
PP-GF30 ~80 ~160 ~0.6
PP-GF40 ~95 ~165 ~0.5

Resin class summary:

  • Amorphous (PC, PMMA, PS, ABS): shrink 0.2–0.7%, dimensionally stable, lower warp, but lower chemical resistance and heat.
  • Semi-crystalline (PP, PE, POM, PA, PPS, PEEK): shrink 1.0–3.0% (except filled PPS/PEEK at 0.2–1.4%), higher chemical/heat resistance, more warp risk.

Glass-filled grades (PA66-GF30, PPS-GF40) shrink less (0.2–0.5%) but need weld-line and fiber-orientation control — the automotive connector in glass-filled PPS / PA66 held ±0.005 mm critical only with that control. Filled compounds also demand a higher melt temperature: glass-filled PP needs 260–280 °C melt to avoid fiber breakage (FirstMold).

Processing windows: melt, mold and drying

The melt and mold temperatures from the property table translate directly into process windows. The table below adds drying requirements and process notes; drying values are typical published supplier recommendations unless marked otherwise.

Resin Melt (°C) Mold (°C) Drying Process notes
PP 220–280 20–80 Not required (check <0.1% moisture) Degradation/yellowing above 290 °C; living hinges need MFR >20
PE 180–280 20–60 Not required HDPE for strength/impact; LDPE-LLDPE for flexibility
PS 200–260 20–60 Not required GPPS clarity; HIPS toughness
ABS 210–250 40–80 80–90 °C, 2–4 h Drying avoids splay; FR grades flow shorter
PC 280–320 80–120 120 °C, 4 h Moisture causes splay and bubbles
PMMA 220–260 60–90 80 °C, 2–4 h Drying avoids silver streaks
PA66 260–300 60–100 80 °C, 4 h Moisture shifts dimensions 0.2–0.5%
PBT 240–270 60–100 110–130 °C Used for keycaps and connectors; dries before molding
POM 180–230 80–120 80 °C, 2 h Thermal degradation risk if overheated
PEEK 350–400 160–200 150 °C, 3 h 260 °C continuous service; high mold temp needed
PPS 300–340 120–160 150 °C, 3 h Inherently V-0; strong glass affinity
PVC 160–190 20–60 Remove surface moisture only Low-shear screw, compression ratio ≤3:1; cycle ~30–60 s

Two process economics worth knowing before you pick. First, high-MFI (melt flow index) grades can cut production time by roughly 30% because they fill and pack faster — FirstMold cites this on its materials page (https://firstmold.com/materials/injection-molding-materials/). Second, reinforced materials accelerate mold wear by about 3× — a glass-filled grade that saves resin cost can cost more in tool maintenance over a multi-million-shot program. Both effects belong in the material decision, not just the datasheet.

Non-absorbent PP / PS / PE / LSR need little or no drying — a scheduling advantage for fast turnaround, and one reason PP and ABS dominate high-volume consumer programs.

Heat, flame and moisture handling

Service temperature sets the floor; flame class sets the regulatory bar. UL94 classes in ascending severity: HB → V-2 → V-1 → V-0 → 5VA/5VB. V-0 means flame-out in ≤10 s with no burning drips — the common bar for enclosures near electronics.

  • ABS / PP / PC: often V-2 to V-0 by grade.
  • PPS / PEI / PEEK: inherently V-0 at 200–260 °C.
  • An NEV charging dust cover ran FR-TPU, UL94 V-0 at 500,000+ units/year.

For extreme environments, FirstMold’s materials page publishes the long-term service bands that define the high-temperature shelf (https://firstmold.com/materials/injection-molding-materials/):

Material Long-term (°C) Short-term (°C) Note
PBI 300–370 No breakdown at 538 Highest practical ceiling
PEI 170 510 Clear, inherently flame-retardant
PEEK 260 >300 Aerospace/medical workhorse
PI (polyimide) −240 to 290 480 Extreme range
PTFE −196 to 260 280 Chemical inertness
UHMWPE Survives liquid nitrogen — Impact at −269 °C
TPU Brittle point −60 >90% elasticity at −40 Cold-ductile elastomer

Moisture handling by resin:

  • PA66: dry 80 °C, 4 h
  • PC: dry 120 °C, 4 h
  • POM: dry 80 °C, 2 h
  • PPS / PEEK: dry 150 °C, 3 h

Decision shortcut by function

  • Need impact + transparency → PC (melt 280–320 °C)
  • Need living hinge → homopolymer PP (melt 200–280 °C, MFR >20, hinge thickness 0.25–0.5 mm)
  • Need wear resistance + tight tolerance → POM or PEEK
  • Need soft-touch overmold → TPU / LSR
  • Need chemical/heat resistance → PPS or PEEK
  • Need lowest cost + light weight → PP (0.90 g/cm³)
  • Need FDA/medical contact → LSR, PEI, USP Class VI PP / ABS / COC
  • Need electrical/chemical with flame class → PPS (inherently V-0)

Materials by industry

The same resin appears in different industries for different reasons. This application map reflects published material guidance from FirstMold’s industry pages and our own program mix:

Industry Typical resins Why these
Automotive PP (~29.9% of program mix), PUR 15.5% Low density, chemical resistance, cost — FirstMold’s automotive page cites this split
Medical PP, ABS, COC (USP Class VI), LSR, PEI Biocompatibility, sterilization, traceability
Consumer electronics ABS, PC, PC/ABS, PBT Impact, flame class, cosmetic surface
EV / battery FR-TPU, PA6-GF30, PPS UL94 V-0, HV insulation, thermal
Aerospace PEEK, PEI 260 °C+ service, strength-to-weight
Industrial / tools POM, PA66, PPS Wear, chemical resistance, precision gears
Personal care / packaging PP, PE, PVC Cost, chemical resistance, color control

The automotive split is a useful sanity check: PP at 29.9% and PUR at 15.5% of the plastic mix (FirstMold: https://firstmold.com/industries/automotive/) is why PP tooling experience is the most transferable capability in the industry. In medical, the USP Class VI shortlist — PP, ABS, COC — plus LSR and PEI covers most devices (https://firstmold.com/industries/medical/). And in keycaps and connectors, PBT carved out a niche on durability and oil resistance (https://firstmold.com/pbt-injection-molding/).

Real programs behind the table

Program Material Tolerance Volume Lead time
Automotive connector Glass-filled PPS / PA66 ±0.005 mm 2M / yr 10 weeks
VR remote housing PC+ABS / TPE ±0.04 mm 800K / yr 9 weeks
Small button POM / ABS ±0.03 mm 5M / yr 12 weeks
Medical ECG button LSR (medical) ±0.03 mm 300K / yr 7 weeks
NEV dust cover FR-TPU (UL94 V-0) — 500K / yr 6 weeks

Two lessons carry across programs. The first is that the tolerance you can hold is set by the resin class before the tool is cut: the ±0.005 mm automotive connector was only quotable because glass-filled PPS/PA66 shrink is low and controllable with weld-line management. The second is lead-time leverage: every program above shipped on a single in-house line — material drying, molding and inspection under one roof — which is why we can quote a 6–12 week window and hold it.

Combining materials: overmolding and inserts

Many production parts are not one resin. Overmolding bonds a soft layer (TPE or LSR) onto a rigid substrate (ABS+PC, PA66), while insert molding casts plastic around a metal part (C11000 copper in the HV busbar, PA6-GF30 at 250,000+ units/year).

The economics are published, not anecdotal. FirstMold cites up to 40% assembly-cost reduction from two-shot molding versus separate parts (https://firstmold.com/two-shot-injection-molding/), and 50% bond-robustness improvement with 30% fewer process steps from insert molding (https://firstmold.com/insert-molding/). Both processes replace an assembly operation with a single molded cycle.

Design notes when combining:

  • Pick a TPE that bonds to your substrate (PC-ABS, PP) — mismatched chemistry delaminates.
  • Account for differential shrink (soft 0.8–1.8% vs rigid 0.4–0.7%) in the overmold gap.
  • Insert molding needs ±0.02 mm placement of the metal insert to avoid flash at PPS / PA66 gates.
  • Preheat metal inserts — FirstMold’s PP insert-molding guidance calls for 110 ± 5 °C inserts, ≥1.5× insert diameter of plastic wall, and 120% packing to lock the insert without cracking it (https://firstmold.com/pp-injection-molding/).

The cost map by resin family

The property table is also a cost map. Price bands below are typical published market ranges — they vary with grade, volume, region and additives, so treat them as selection bands, not quotes:

Resin Typical price ($/kg) Density (g/cm³) Relative part-cost note
PP 1–2.5 0.90 Value floor; lightest common resin
PE 1–1.8 0.94 Cheapest commodity; soft grades
PS 1.2–2 1.05 Rigid, cheap, brittle
PVC 1–1.5 1.38 Cheap but dense; V-0 rigid grades
ABS 1.5–3 1.05 Default enclosure resin
PMMA 2–3 1.18 Clarity at moderate cost
POM 2–3.5 1.41 Precision wear parts
PC 2.5–4 1.20 Impact + transparency
PA66 3–6 1.14 Structural, bearings
TPU 3–5 1.10–1.20 Soft-touch elastomer
PPS 8–15 1.35 V-0 chemical/heat workhorse
PEEK 50–100 1.32 Performance ceiling

The total part cost, though, is not the resin price. FirstMold publishes the standard split for an injection molded part: raw material 40–60%, processing 20–35%, mold 15–25%, post-processing 5–20% (https://firstmold.com/materials/injection-molding-materials/). Two consequences follow. First, a resin that is 5× more expensive per kilo only moves the part price meaningfully if material dominates the split — which it does for heavy, high-volume parts, not for thin-wall housings. Second, cycle time and mold cost often outweigh resin price: a high-MFI grade that cuts cycle time 30% can beat a cheaper resin on total cost per part.

When a quote looks expensive, check whether an engineering grade was specified where a commodity resin would do — moving PEEK to PPS can cut resin cost 5–10× while holding 200 °C+ service.

Regulatory and sustainability reading

Resin choice interacts with compliance:

  • RoHS / REACH: restrict heavy metals and SVHCs — relevant for ABS, PC, PPS imported to the EU.
  • UL94: flame class on the print for enclosures near electronics (V-0 = flame-out ≤10 s, no drips).
  • Recycled content: PP and ABS take post-consumer regrind at 10–30% with minor property loss; PEEK and PPS are rarely recycled in volume.
  • Medical / food: LSR and PEI are the biocompatible choices (the MRI balun ran PEI at 15,000+ units/year).
  • Color stability: PVC and FR-ABS programs with strict color control depend on the additive package — specify the color standard in the RFQ, not after tooling.

Flame class deserves one extra note: specifying V-0 after the tool is cut can force a different grade with different shrinkage and flow, which invalidates the original tool design. Call the flame class on the drawing before the DFM, and let the tool be quoted against the actual grade.

Common material-selection mistakes

  • Over-specifying performance: PEEK where PPS or PA66-GF30 would do adds 5–10× resin cost with no functional gain.
  • Ignoring moisture sensitivity: PA and PC molded without drying produce splay, voids and dimension drift of 0.2–0.5%.
  • Choosing semi-crystalline without designing for shrink: a tool cut to amorphous shrink values cannot hold tolerance in PP or POM.
  • Deciding flame class too late: V-0 grades differ in shrink, flow and color; late changes force tool rework.
  • Cost-only selection: the cheapest resin can be the most expensive part if it needs a slower cycle or wears the tool 3× faster.
  • Skipping chemical compatibility: an application with solvents, fuels or cleaners needs the chemical-resistance check before tooling, not after field failures.

Frequently Asked Questions

1. Which plastic is the cheapest to injection mold? PP is the value floor — $1–2.5/kg and 0.90 g/cm³ density, so you buy more parts per kilo. PE and PS are close. The cheapest resin per part, however, also depends on cycle time and tool wear; a high-MFI grade can cut production time ~30%.

2. Which resin holds the tightest tolerance? Amorphous resins shrink 0.2–0.7% (PC, PMMA, PS), which is why they hold tighter tolerances than semi-crystalline resins. Glass-filled grades (PA66-GF30, PPS-GF40) shrink as little as 0.2–0.5% and can hold ±0.005 mm on critical features with weld-line control.

3. What does UL94 V-0 mean? V-0 means the specimen stops burning within 10 seconds of flame removal with no burning drips. The UL94 severity ladder runs HB → V-2 → V-1 → V-0 → 5VA/5VB. PPS, PEEK and PEI are inherently V-0; ABS, PP and PC need FR grades.

4. Can I use PP for a living hinge? Yes — PP is the classic living-hinge material, but it must be homopolymer PP with MFR above 20 g/10 min. Keep the hinge 0.25–0.5 mm thick with a transition arc of at least 0.5 mm and width at least 6× the thickness (FirstMold).

5. Why does my nylon part change dimensions in humid conditions? PA66 absorbs moisture, which swells the part — dimension shifts of 0.2–0.5% are typical. Dry the resin (80 °C, 4 h) before molding and, for humid end-uses, design the tool against conditioned dimensions.

6. Is PEEK worth the price? Only when the application demands it: 260 °C continuous service, aggressive chemicals, or wear-critical medical/aerospace use. If the part sees 200–240 °C, PPS delivers much of the performance at 5–10× lower resin cost.

7. What is the difference between amorphous and semi-crystalline resins? Amorphous resins (PC, PMMA, PS, ABS) shrink 0.2–0.7%, warp less and hold tighter tolerances, but have lower chemical and heat resistance. Semi-crystalline resins (PP, PE, POM, PA, PPS, PEEK) shrink 1.0–3.0%, resist chemicals and heat better, but warp more and need more draft.

8. Which resin should I pick for transparent parts? PC for impact plus clarity, PMMA for optical-grade clarity, PS for cheap clear parts, COC for medical. All need care with gate location to avoid flow marks, and drying to avoid splay.

9. Can I use recycled resin? PP and ABS take post-consumer regrind at 10–30% with minor property loss — common for non-cosmetic, non-critical parts. PEEK and PPS are rarely recycled in volume, and recycled content can shift color and impact performance, so verify the grade’s properties.

10. What is the best resin for soft-touch overmolding? TPE on PC/ABS or PP substrates for consumer parts, LSR for medical and high-temperature use. The bond depends on chemistry matching, not just hardness — a TPE formulated for PP will delaminate from PC.

11. Which materials are biocompatible? LSR and PEI are the workhorse medical choices, joined by USP Class VI grades of PP, ABS and COC. Programs requiring ISO 10993 or FDA contact need the material certificate at the resin-lot level, not just the generic grade name.

12. POM or PA66 for gears? POM holds precision dimensions with low moisture uptake — the classic gear material. PA66 absorbs moisture but offers higher toughness and wear resistance in impact-heavy applications. Both hold ±0.03–0.05 mm in production with steel-safe tooling.

Sources

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Written by

Ray Chan

Manufacturing Engineer · Custom Manufacturing Specialist. Ray helps global importers and integrators source factory-direct plastic parts and tooling.

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