Ask three engineers which plastic to use for a molded part and you may get three different answers — usually whichever material they have had the best experience with. But material selection is not a matter of preference. It is a set of trade-offs between strength, heat resistance, chemical exposure, dimensional stability, appearance, and cost, and the correct answer depends entirely on what your part has to survive.

ABS, polycarbonate (PC), and polypropylene (PP) are three of the most widely used injection molding thermoplastics in the world, and they sit at three very different points on that trade-off map. ABS is the balanced all-rounder with the best surface finish. PC is the high-performance choice for impact and transparency. PP is the low-cost chemical-resistant workhorse.

This guide compares them head to head across every property that matters, then gives you a practical decision framework for choosing the right one.

1. The Three Materials at a Glance

Before getting into detail, here is how the three compare at a high level:

The three occupy genuinely different positions. ABS wins on surface finish and processability, PC on impact and heat, PP on cost and chemical resistance. Very few parts are equally well served by all three — which is good news, because it means the decision is usually clearer than it first appears.

2. ABS: The Balanced All-Rounder

ABS (acrylonitrile butadiene styrene) is a terpolymer that combines three monomers: acrylonitrile contributes chemical resistance and heat stability, butadiene provides impact toughness, and styrene delivers rigidity, gloss, and processability. Adjusting the ratio lets compounders tune the material from soft and rubbery to hard and glossy.

Strengths. ABS is rigid and dimensionally stable, with low and predictable shrinkage of 0.4–0.7%. It takes an excellent surface finish and is the easiest of the three to paint, plate, and texture — which is why it dominates automotive interior trim, appliance housings, and consumer electronics. It processes easily across a wide melt window and is forgiving of minor process variation.

Limitations. ABS has only moderate impact resistance compared with PC, and it degrades under UV exposure, yellowing and embrittling outdoors unless painted or capped with a weatherable layer. Its heat deflection temperature of 80–110°C rules out high-temperature applications, and it is vulnerable to stress cracking when exposed to certain chemicals and solvents.

Typical applications. Automotive interior trim and dashboards, appliance and power-tool housings, consumer electronics enclosures, printer and keyboard components, toys, and non-contact medical device housings.

3. PC: The High-Performance Option

Polycarbonate is an amorphous engineering thermoplastic known for two properties that are rarely found together: exceptional impact strength and optical clarity. Its notched Izod impact of 600–900 J/m is several times that of ABS, and it is available in fully transparent grades.

Strengths. PC offers the highest impact resistance of any common rigid thermoplastic, excellent heat resistance (120–140°C), good dimensional stability, and optical clarity for lenses, light pipes, and glazing. It also has better inherent fire performance than ABS and is available in flame-retardant and medical grades.

Limitations. PC is the most expensive of the three. It is more difficult to process — it absorbs moisture and must be thoroughly dried before molding to avoid hydrolysis and splay. It is also prone to stress cracking under load in the presence of certain chemicals, requires higher processing temperatures, and is harder to plate or paint than ABS. Its notch sensitivity means sharp internal corners matter more in PC design.

Typical applications. Safety glasses and face shields, machine guards, lighting lenses and diffusers, transparent housings and reservoirs, automotive lighting, glazing, and high-impact electronic enclosures.

4. PP: The Low-Cost Workhorse

Polypropylene is a semi-crystalline polymer and the lightest of the three at roughly 0.90 g/cm³ — it even floats on water. It is the most-produced plastic in the world by volume, largely because it is inexpensive and chemically robust.

Strengths. PP has excellent chemical resistance across a broad range of acids, bases, and solvents, which makes it the default for laboratory consumables, chemical containers, and fluid-path components. It has very good fatigue resistance, which is what makes living hinges possible, and it is autoclavable. It is also the lowest-cost of the three and the lightest.

Limitations. PP shrinks substantially more than ABS or PC — 1.0–2.5% versus 0.4–0.7% — which makes tight tolerances harder to hold and increases warpage risk. It has lower stiffness and strength than either alternative, poor low-temperature impact in homopolymer grades (copolymers improve this), and it is difficult to paint or bond without surface treatment such as flame or plasma treatment.

Typical applications. Living hinges and closures, chemical and food containers, laboratory consumables, automotive bumpers and battery cases, fluid-path medical components, and household goods.

5. Head-to-Head Property Comparison

Here is the detailed comparison across the properties that most often drive selection:

Reading the table, a pattern emerges: PC wins nearly every performance category, ABS wins the finishing and processability categories, and PP wins on cost and chemical resistance. Your part's priorities determine which column matters.

6. Heat Resistance Compared

Heat is often the first filter that eliminates a candidate. ABS and PP both have heat deflection temperatures in the 80–110°C range, while PC extends to 120–140°C.

In practice, this means ABS and PP are suitable for consumer and indoor applications but will soften in under-hood automotive environments, near heat-generating electronics, or in any application involving hot liquids or steam sterilization beyond what the grade allows. PC handles those conditions comfortably.

It is worth noting that filled and reinforced grades change this picture substantially. Glass-filled PP can push heat deflection well above 120°C, and glass-filled ABS or PC extend further still. If your part is temperature-limited, a filled grade is often a cheaper fix than moving to a premium base resin.

For sterilizable medical devices, PP's autoclavability at around 121°C is a decisive advantage despite its lower mechanical performance — one of the clearest examples of a single requirement overriding the rest of the comparison.

7. Chemical and Environmental Resistance

Chemical exposure is where PP dominates and PC is most vulnerable.

• PP resists most acids, bases, alcohols, and aqueous solutions, and has excellent resistance to environmental stress cracking. It is attacked by strong oxidizing acids and some hydrocarbons at elevated temperature, and it swells in chlorinated solvents and aromatics.
• ABS handles dilute acids, alkalis, and aliphatic hydrocarbons reasonably well but is attacked by ketones, esters, aldehydes, and chlorinated solvents. Contact with certain chemicals under load causes stress cracking, which is a common field-failure mode in ABS parts.
• PC has the narrowest chemical compatibility. It is particularly vulnerable to stress cracking when under load in contact with oils, greases, and many organic solvents, and it is attacked by strong alkalis and amines. This is why PC parts in contact with lipids or aggressive cleaning agents require careful grade selection or a protective coating.

For outdoor applications, none of the three is naturally excellent. ABS yellows and embrittles under UV; PP degrades unless UV-stabilized or carbon-black-filled; PC has the best inherent resistance of the three but still yellows over time without a UV-stabilized or hard-coated grade. ASA or UV-stabilized grades are usually the better answer for long-term outdoor exposure.

8. Cost Comparison

Material price per kilogram is the most visible cost, but the more useful number is cost per part, which accounts for density and processing.

• PP is the cheapest both per kilogram and per part. Its low density (0.90 g/cm³) means you buy roughly 15% less material by weight than ABS for the same volume, and its low processing temperature keeps cycle times short and energy use down.
• ABS is mid-priced. It processes easily and cycles quickly, which helps offset a higher per-kilogram cost than PP.
• PC is the most expensive, typically costing meaningfully more per kilogram than ABS, and it adds processing cost through mandatory drying, higher melt temperatures, and often longer cycle times.

However, material is usually only a minority of total part cost — tooling, machine time, and secondary operations often dominate. A material that eliminates a painting step (ABS with molded-in color) or avoids a secondary bonding operation can be cheaper overall than a cheaper resin requiring extra finishing. This is why injection molding material selection should be evaluated on total part cost, not resin price alone.

9. Shrinkage and Dimensional Stability

Shrinkage determines how easily you can hold tolerance, and the three behave very differently.

ABS and PC are both amorphous with low, predictable shrinkage of 0.4–0.7%. They do not crystallize, so their dimensions remain stable across normal service temperatures and they hold tight tolerances well. This makes them the natural choice for parts with critical mating dimensions, snap fits requiring consistent deflection force, or multi-component assemblies.

PP is semi-crystalline and shrinks 1.0–2.5% — roughly two to four times more. That higher shrinkage brings three practical consequences:

1. Tighter tolerances are harder and more expensive to hold, particularly on larger parts.
2. Warpage risk increases substantially, because differential cooling across a semi-crystalline part produces differential crystallinity and therefore differential shrinkage.
3. Gate location and wall uniformity matter far more, since flow-direction shrinkage differs from transverse shrinkage.

None of this disqualifies PP — it simply means the design must accommodate it. Specifying realistic tolerances per ISO 20457:2018, keeping walls uniform, and validating with mold flow analysis are essential when molding PP to tight specifications.

10. How to Choose: A Practical Decision Framework

Work through these questions in order. In most cases, one material will separate itself from the others within the first three.

Step 1: Does the part need transparency? If yes, PC is the only real option of the three. If no, continue.

Step 2: What temperature will the part see in service? Above roughly 110°C continuous, choose PC (or a filled grade). Below that, ABS and PP both remain viable.

Step 3: What chemicals will it contact? Aggressive solvents, oils, or a broad pH range favor PP. Mild household chemicals are fine for ABS. Avoid PC where stress cracking is a risk under load.

Step 4: Does it need a high-quality painted, plated, or textured finish? If appearance is critical, choose ABS. PC is paintable but harder to finish, and PP requires surface treatment.

Step 5: Are tolerances tight? If you need tight, stable dimensions, prefer ABS or PC. PP can hold tolerance but requires more design care and validation.

Step 6: Is cost the dominant constraint? For high-volume parts with modest performance requirements, PP is usually the answer.

Step 7: Does the part need exceptional impact resistance? Safety equipment, guards, or drop-prone products point to PC.

Quick selection guide:

11. Common Selection Mistakes

• Choosing on material price alone. A cheaper resin that requires painting, surface treatment, or produces higher scrap is not cheaper per finished part.
• Ignoring shrinkage until tooling is cut. PP's 1.0–2.5% shrinkage must be designed for from the start; discovering it at first article means re-cutting steel.
• Assuming PC is always better because it is stronger. PC's chemical sensitivity, cost, and processing difficulty make it the wrong choice for many parts.
• Specifying ABS for outdoor use without UV protection. It will chalk, yellow, and embrittle.
• Overlooking blends and filled grades. An ABS/PC blend or glass-filled PP often hits requirements that no single base resin meets cleanly.
• Not prototyping in the production material. Prototype parts printed in a different resin do not reveal shrinkage, warpage, or chemical behavior.

12. Blends, Filled Grades, and Alternatives

When none of the three base resins is a clean fit, these variants usually are:

• ABS/PC blend — combines ABS's processability and finish with PC's higher impact and heat resistance. A common choice for automotive and electronics housings that need more performance than ABS but cannot justify full PC.
• Glass-filled PP — dramatically increases stiffness and heat deflection while retaining chemical resistance and low cost. Excellent for structural automotive and appliance parts.
• Flame-retardant grades — available in all three, required for mains-powered electronics (see UL 94 ratings).
• UV-stabilized grades — carbon-black or additive-stabilized PP and ASA for outdoor exposure.
• TPO and TPE overmolds — soft-touch grips overmolded onto rigid ABS or PP substrates.
• Beyond these three — nylon (PA) for wear and high load, POM for precision gears and bearings, PEEK for extreme temperature and medical implants.

If your assembly mixes materials, we also support die casting for metal structural components and heat sinks.

13. Get a Material Recommendation for Your Part

There is no universally "best" plastic — only the best plastic for a specific part with a specific set of requirements. ABS, PC, and PP each dominate their own territory, and the decision becomes straightforward once you know which requirements are non-negotiable.

The most reliable way to decide is to share your part's operating environment, mechanical loads, cosmetic requirements, and volume with an experienced molder, then validate the choice with a prototype molded in the actual production resin.

Our engineering team reviews material selection as part of every DFM review, and we prototype in your production material so shrinkage, warpage, and finish are validated before tooling. We support plastic injection molding, in-house custom mold making, and rapid prototyping to take your part from material selection through validated production. Material and testing references from ASTM International and the Plastics Industry Association support specification and validation.

Learn more about our company and capabilities.