ABS Injection Molding: Grade Comparison, Properties, Drying & Process Guide

Acrylonitrile Butadiene Styrene (ABS)—supplied under benchmark trade names such as Cycolac (SABIC), Terluran / Novodur (INEOS Styrolution), and Polylac (Chi Mei)—is the default amorphous engineering thermoplastic for consumer electronics enclosures, appliance housings, power-tool bodies, and interior automotive trim.

Each monomer in the terpolymer contributes a distinct engineering property: Acrylonitrile (15–35%) provides chemical resistance, heat stability, and surface hardness; Butadiene (5–30% dispersed rubber phase) delivers impact toughness and low-temperature ductility; and Styrene (40–60%) provides high surface gloss, rigidity, and low-viscosity moldability. Because ABS is amorphous, it exhibits low, isotropic mold shrinkage (0.4%–0.7%), holds tight dimensional tolerances without post-mold warpage, and accepts adhesives, ultrasonic welding, painting, and chrome electroplating better than almost any other plastic.

Use this guide alongside the material selection guide and polycarbonate guide to select the right ABS grade and avoid common thermal, UV, and flame-retardant pitfalls.

1. ABS Grade Comparison Matrix: GP-ABS vs High-Heat vs FR-ABS vs PC/ABS

Writing generic “ABS” on a part print leaves impact strength, heat deflection temperature, and flammability open to wide interpretation. Specify the exact sub-grade family based on your operating environment:

Property / Specification	General-Purpose ABS (GP-ABS)	High-Impact ABS (HI-ABS)	High-Heat ABS (HH-ABS, $\alpha$-methylstyrene)	Flame-Retardant ABS (FR-ABS)	PC/ABS Alloy (e.g., Cycoloy / Bayblend)
Specific Gravity (g/cm³)	1.04 – 1.06	1.02 – 1.04	1.05 – 1.07	1.18 – 1.22	1.12 – 1.18
Tensile Yield Strength (MPa)	42 – 48 MPa	34 – 40 MPa	45 – 52 MPa	36 – 42 MPa	52 – 62 MPa
Flexural Modulus (GPa)	2.2 – 2.6 GPa	1.8 – 2.1 GPa	2.4 – 2.8 GPa	2.1 – 2.4 GPa	2.3 – 2.7 GPa
Notched Izod Impact (23 °C, J/m)	180 – 260 J/m	320 – 480 J/m	120 – 180 J/m	150 – 220 J/m	450 – 650 J/m
Heat Deflection Temp (HDT @ 1.8 MPa)	80 – 88 °C (unannealed)	76 – 82 °C	98 – 110 °C	75 – 84 °C	105 – 125 °C
UL 94 Flame Rating (@ 1.5–2.0 mm)	UL 94 HB	UL 94 HB	UL 94 HB	UL 94 V-0 / 5VA	UL 94 HB or V-0 (grade-dependent)
Mold Shrinkage (mm/mm)	0.4% – 0.7%	0.5% – 0.8%	0.4% – 0.6%	0.4% – 0.6%	0.5% – 0.7%
Primary Buyer Use Case	Indoor consumer housings, toys, cosmetic bezels, painted or chrome-plated trim	Power tool housings, luggage shells, protective helmets, cold-drop enclosures	Automotive dash panels, HVAC vents, hair-dryer and coffee-maker housings	Power bricks, router enclosures, indoor electrical junction boxes	Laptop frames, medical carts, EV battery modules needing higher heat + impact than FR-ABS

(Note: A specialized Electroplating-Grade ABS—with controlled ~18–22% uniformly dispersed polybutadiene rubber particles that etch cleanly in chromic/sulfuric acid to form microscopic mechanical anchor pores—must be specified whenever parts undergo decorative chrome/nickel plating.)

2. Where ABS Falls Short (When to Reject Unmodified ABS)

Before locking in ABS, check four environmental failure modes:

1. UV Degradation & Chalking Outdoors: Sunlight (UV-B) attacks the unsaturated double bonds in the butadiene rubber phase, causing unmodified ABS to turn yellow, chalk, and lose over 50% of its impact strength within months of outdoor exposure. For outdoor enclosures, specify ASA (Acrylonitrile Styrene Acrylate)—which replaces butadiene rubber with UV-stable acrylate rubber while running in the exact same ABS mold shrinkage (0.4–0.7%)—or apply a UV-blocking paint coat.
2. Low Continuous Heat Limit (< 80 °C): Standard GP-ABS softens and warps when left inside a closed vehicle cabin in summer (85–105 °C) or mounted near heat sinks. Upgrade to High-Heat ABS (HH-ABS) or PC/ABS.
3. Environmental Stress Cracking (ESC) in Solvents: Ketones (acetone, MEK), esters, aromatic hydrocarbons, certain threadlockers (Loctite), and PVC plasticizer migration cause ABS to craze and crack rapidly under molded-in tensile stress. If chemical resistance is primary, switch to semi-crystalline polypropylene (PP), nylon, or PBT.
4. Flammability: Unmodified ABS burns readily (UL 94 HB) with heavy black soot. If your product requires UL 94 V-0, either specify FR-ABS (for indoor moderate-heat housings) or FR PC/ABS (when both V-0 flame compliance and > 95 °C heat resistance are required).

3. ABS Injection Molding Processing Window (GP-ABS vs FR-ABS)

Published processing guidelines from INEOS Styrolution, SABIC, and Chi Mei separate standard ABS from thermally sensitive flame-retardant ABS (FR-ABS):

Processing Parameter	Standard / High-Impact ABS (GP / HI)	High-Heat / Plating ABS (HH)	Flame-Retardant ABS (FR-ABS, UL94 V-0)
Pre-Drying (Desiccant / Hot Air)	80–85 °C for 2–4 hours	85–90 °C for 3–4 hours	75–80 °C for 2–4 hours
Max Moisture Before Molding	≤ 0.05% – 0.10% (≤ 0.02% for chrome-plating grades)	≤ 0.05%	≤ 0.05% – 0.08%
Melt Temperature Window	210–250 °C (410–480 °F)	240–265 °C (465–510 °F)	190–220 °C (375–430 °F — Strict Cap!)
Barrel Residence Time Limit	≤ 5–8 minutes	≤ 5–6 minutes	≤ 3–4 minutes (Decomposes rapidly if held hot)
Mold Temperature Window	50–75 °C (120–165 °F)	65–85 °C (150–185 °F)	50–70 °C (120–160 °F)
Perimeter Vent Depth	0.025–0.050 mm (0.001–0.002 in)	0.025–0.050 mm	0.030–0.050 mm (clean frequently for FR plate-out)

Three Critical DFM & Process Rules for ABS Buyers:

• Keep Rib-to-Wall Thickness at 50%–60% to Prevent Sink Marks: Because ABS frequently forms high-gloss or fine-textured Class A exterior housings, sink marks opposite internal ribs and screw bosses are immediately visible. Limit rib base thickness to 50%–60% of the nominal wall (e.g., a 1.2–1.5 mm rib on a 2.5 mm wall) and core out thick boss bases.
• Never Overheat FR-ABS Above 225 °C: Flame-retardant ABS contains brominated additives that thermally decompose above 225–230 °C, creating black/brown burn streaks on the part and releasing corrosive acidic gas that pits unprotected P20 mold steel. Require 420SS stainless cavity inserts or corrosion inhibitor wiping when running high-volume FR-ABS.
• Low-Stress Molding for Electroplating & Painting: If ABS parts will be chrome-plated or solvent-painted, molded-in shear stress causes blistering and paint crazing. The molder must run a hotter melt (240–255 °C), a hotter mold (65–80 °C), and a slower injection fill speed to minimize frozen-in molecular orientation.

Buyer FAQs

Does ABS plastic need to be dried before injection molding?

Yes—ABS is mildly hygroscopic (absorbing 0.2%–0.4% ambient moisture) and must be dried at 80–85 °C (175–185 °F) for 2 to 4 hours until moisture content is below 0.05%–0.10% (≤ 0.02% for electroplating grades). Molding undried ABS does not sever polymer chains as severely as in polycarbonate or nylon, but trapped steam creates silver splay streaks, surface blisters, and weld-line delamination that ruin Class A cosmetic housings and cause blisters during chrome plating.

What is the mold shrinkage rate of ABS?

Unfilled ABS has a low, isotropic mold shrinkage rate of 0.004 to 0.007 mm/mm (0.4% to 0.7%), with 0.5% (0.005 in/in) serving as the standard nominal tooling shrinkage for general-purpose grades (15–30% glass-filled ABS shrinks only 0.1%–0.3%). Because ABS is amorphous and lacks a crystalline phase transition, it shrinks uniformly in both flow and cross-flow directions, making it far less prone to post-mold warpage than semi-crystalline polypropylene or nylon.

When should I specify PC/ABS instead of pure ABS?

Upgrade from pure ABS to a PC/ABS alloy when your part requires higher heat deflection resistance (105–125 °C vs 80–85 °C for GP-ABS), 2× to 3× higher Notched Izod impact toughness (450–650 J/m), thin-wall UL 94 V-0 flame compliance (at 1.2–1.5 mm) without the thermal instability of brominated FR-ABS, or ductile sub-zero drop performance down to -30 °C. Pure ABS remains the better choice when lowest resin cost (~25–35% cheaper than PC/ABS) and ease of electroplating are the primary goals.

Can ABS be used for outdoor injection-molded parts?

Unmodified ABS is unsuitable for direct outdoor sunlight because UV radiation breaks down its butadiene rubber phase, causing yellowing, surface chalking, and brittle impact failure within months. If an outdoor housing is already designed for ABS shrinkage (0.4%–0.7%), specify ASA (Acrylonitrile Styrene Acrylate)—which drops straight into an ABS-shrunk mold while providing 10× better UV weatherability without painting.

Disclaimer

PlasticsTechnologyAlliance.com is an independent buyer resource. It does not manufacture parts, sell materials, or certify suppliers. Mechanical properties and processing windows vary across general-purpose, high-heat, and flame-retardant ABS grades; always verify specifications against the manufacturer’s grade-specific datasheet.