How to Choose Between Polycarbonate, Polypropylene, and ABS: A Practical Decision Checklist

If you're staring at a spec sheet trying to decide between polycarbonate (PC), polypropylene (PP), and ABS—you're not alone. Over the past few years, I've reviewed hundreds of material selection decisions for our production runs. And honestly? A lot of them came back because the choice looked good on paper but didn't hold up in the real world.

This checklist is for anyone who needs to pick one of these three thermoplastics and actually live with the consequences—that means engineers, procurement folks, and quality managers. I'll walk you through the five factors I check every time, plus a few gotchas that cost us real money.

Who This Checklist Is For

Use this when you're choosing a material for a molded or extruded part that needs to balance strength, heat resistance, chemical resistance, and cost. It's not for high-volume commodity items like bags or bottles—that's a different conversation. Here, we're talking about enclosures, housings, automotive interior parts, piping, and similar applications.

Step 1: Check the Thermal Requirements—Start Here

This is the most common reason I see material choices fail. You'd be surprised how many specs get approved without anyone checking the continuous use temperature.

Polycarbonate has a glass transition temperature (Tg) around 147°C and can handle continuous use up to about 125°C. That's way higher than the other two. But—and this is a big but—PC is susceptible to hydrolysis above 60°C in humid environments. So if your part sees both heat and moisture, PC might not be your friend.

Polypropylene melts at around 160-170°C (melting HDPE is similar but lower, around 130°C for comparison). PP is semicrystalline, so it softens gradually rather than hitting a sharp glass transition. It's fine up to about 100°C in air, but drops off significantly in contact with certain chemicals.

ABS is amorphous, with a Tg around 105°C. It's not great above 80°C continuous. I once rejected a batch of ABS housings that warped because the ambient temperature near a motor hit 85°C. The vendor claimed it was 'within industry standard.' We sent it back anyway.

Quick rule of thumb: If your part will see sustained heat above 90°C, PC is probably your pick. If it's under 80°C, all three can work—but PP usually wins on cost and chemical resistance.

Step 2: Evaluate Mechanical Properties—Strength vs. Impact

People love to cite tensile strength and flexural modulus, but the real question is: what happens when it gets dropped, hit, or stressed over time?

Polycarbonate is the impact champion. Notched Izod impact strength is around 600-850 J/m—way higher than PP or ABS. It doesn't shatter. In our Q1 2024 quality audit, we tested PC enclosures dropped from 1.5 meters onto concrete. Zero failures. ABS enclosures? About 60% survived, and the rest cracked at the corners.

Polypropylene has decent impact resistance, especially at room temperature, but it gets brittle below 0°C. Its tensile strength is lower (around 30-40 MPa vs. 60-70 MPa for PC). But it's flexible—it won't crack under repeated bending like PC or ABS might.

ABS sits in the middle. Good impact resistance at room temp, decent tensile strength (40-50 MPa), but poor UV resistance without additives. It also suffers from fatigue cracking under cyclic loads—something I learned the hard way when a batch of ABS clips failed after 10,000 cycles instead of the specified 50,000.

I ran a blind test with our engineering team: same part geometry, PC vs. PP vs. ABS. 80% identified PC as 'more rugged' without knowing which was which. The cost increase was about $0.80 per piece. On a 10,000-unit run, that's $8,000 for measurably better durability.

Step 3: Consider the Chemical Environment—This One's Tricky

This is where I see the most mistakes. People look at a chemical resistance chart, see 'good' for all three, and call it done. But real-world exposure is rarely a single chemical at a controlled concentration.

Polypropylene is the chemical resistance king among these three. It's resistant to most acids, bases, and organic solvents at room temperature. That's why it's everywhere in chemical tanks and piping. But it swells in aromatic hydrocarbons and chlorinated solvents.

Polycarbonate is chemically weak. It's attacked by even mild solvents, including some cleaning agents. I still kick myself for not catching this earlier: we specified PC for a medical device housing that had to be wiped with isopropyl alcohol daily. After six months, the surface crazed—a network of tiny cracks. If I'd caught it, we'd have switched to ABS or added a coating.

ABS handles weak acids and bases fine, but it dissolves in ketones (acetone) and is attacked by concentrated acids. It also suffers from stress cracking in the presence of certain oils and greases.

Protip: If your part will regularly contact cleaning solvents, lubricants, or fuels, lean toward PP. If it needs clarity and heat resistance, PC—but plan for a protective coating. For general-purpose indoor use with occasional cleaning, ABS is often good enough.

Step 4: Assess Processing and Cost—Not All Parts Are Created Equal

Material cost per kg is only part of the picture. I've seen buyers pick a cheaper material only to spend way more on tooling, cycle time, and rejects.

Polypropylene is easy to injection mold, with good flow and low shrinkage (1.5-2.5%). Tooling costs are moderate. But it has a narrow processing window—too hot and it degrades, too cold and it doesn't fill the cavity. Scrap is recyclable, though. Raw material cost: roughly $1.20-1.80/kg for homopolymer.

ABS is also easy to mold, with good surface finish straight from the tool. Shrinkage is lower (0.4-0.7%). Tooling cost is similar to PP. Cycle times are slightly longer because ABS needs more cooling time to avoid warpage. Cost: about $1.80-2.50/kg.

Polycarbonate is harder to process. It needs higher temperatures (280-320°C), must be dried thoroughly before molding (moisture causes bubbles and brittleness), and has higher shrinkage (0.5-0.7%). Tooling can be 10-20% more expensive because of tighter tolerances. Cost: $2.50-4.00/kg.

Here's what I tell procurement: calculate the total cost per part, not per kg. In one project, PP looked 30% cheaper per kg, but because we needed thicker walls to meet impact specs, the final part weight was higher. ABS ended up being the cheapest per part by about 12%. PC was still the most expensive, but for that application—it was the only one that passed our drop test.

Step 5: Factor in Sustainability—It's Not Just About Recyclability

Every material supplier now claims their products are 'sustainable,' and I've learned to ask tough questions. According to industry-standard data (ASTM D7611 for resin codes):

• PP (resin code 5) is widely recyclable. Post-industrial scrap is commonly reground and reused. Post-consumer recycling rates are lower but improving.
• ABS (not typically assigned a resin code) is recyclable but less common in municipal streams. Many converters close-loop their own scrap.
• PC (resin code 7, 'other') is technically recyclable but infrastructure is limited. Some grades now include recycled content.

If your customer is asking for a polycarbonate vs polypropylene vs abs comparison from a green angle, here's the honest answer: PP usually wins for single-use or short-lifecycle applications because it has a clearer recycling pathway. PC wins for durable goods because the longer lifespan offsets its higher production impact. ABS sits in the middle—it's a common material for consumer electronics housings that are rarely recycled.

One thing I'm careful about: I won't claim a material is '100% environmentally friendly' without lifecycle data. And neither should you.

Watch Out for These Traps

Trap 1: Picking ABS for outdoor use without UV stabilizers. I've rejected multiple batches because the surface degraded within a year. ABS needs UV additives or a coating for outdoor exposure.

Trap 2: Using PC in frequent contact with food without checking FDA/NSF compliance. Standard PC can leach BPA. There are BPA-free grades, but they cost more.

Trap 3: Assuming PP is 'cheap plastic.' Glass-filled PP can have mechanical properties comparable to some ABS grades. Don't write it off based on perception.

Trap 4: Ignoring the melting point for HDPE. Not the same as PP. Melting HDPE is around 130°C—lower than PP. If your spec says 'melting HDPE' but you mean PP, that's a mismatch. (I've seen it on specs. Twice.)

At the end of the day, no single material is 'best.' The right choice depends on what you're optimizing for: heat, impact, chemicals, cost, or sustainability. And anyone who tells you one option dominates everything? They probably haven't had to reject a batch and explain why to their boss.