PC vs ABS vs Nylon for High-Impact Load-Bearing Parts
You’re designing a part that needs to take a beating — repeated impacts, a constant static load, year-round service without creeping or cracking. Which plastic do you reach for?
Here’s the thing: no single material dominates all three requirements. Nylon wins on tensile strength and creep. PC wins on impact resistance and dimensional stability. ABS wins on cost and surface finish. The right choice depends on which of those matters most in your application. I’ve stood on the shop floor watching all three fail in the wrong use case — let me walk through the data.
What “Load-Bearing” Actually Means
Load-bearing in plastic parts means two different things that engineers sometimes lump together:
Static load — the part sits under a constant force. Think a bracket holding a motor, or a housing supporting internal components over years. The enemy here is creep: gradual deformation under sustained stress.
Dynamic/impact load — the part gets hit, dropped, or vibrated repeatedly. Think a power tool housing hitting concrete, or an automotive latch cycled ten thousand times. The enemy here is crack propagation and fatigue.
A part like an automotive pedal bracket or a lawn equipment housing sees both. That’s when material selection gets interesting.
The Three Contenders
| Property | ABS | PC | PA6 | PA66 |
|---|---|---|---|---|
| Tensile Strength | 40-50 MPa | 60-70 MPa | 75-90 MPa | 80-100 MPa |
| Notched Izod | 150-350 J/m | 600-900 J/m | 50-80 J/m | 60-100 J/m |
| Flexural Modulus | 2.0-2.6 GPa | 2.1-2.4 GPa | 2.8-3.5 GPa | 3.0-3.8 GPa |
| Creep @ 50% Load (1000h) | 1.2% | 0.8% | 1.5% (wet) | 0.9% (wet) |
| Water Absorption | 0.3% | 0.15% | 1.5-2.5% | 1.0-1.8% |
| Cost Index | 1.0x | 1.4x | 1.5x | 1.8x |
Let’s break down what these numbers actually mean on the press.
Nylon: The Load-Bearing Champion
If your part carries a sustained load — a structural bracket, a gear housing, a pulley — nylon is your baseline. PA66 hits 80-100 MPa tensile strength, nearly double ABS. That’s not academic. That’s the difference between a bracket that holds a 15 kg motor for five years and one that creeps 2 mm in six months.
The creep catch. Nylon’s creep data looks good — 0.9% at 50% load after 1000 hours for PA66. But that number assumes dry-as-molded condition. In a humid environment, PA6 absorbs 1.5-2.5% water by weight. That water plasticizes the material and drops the tensile modulus significantly. I’ve seen nylon brackets that passed every FEA simulation fail in the field because nobody accounted for 60% humidity in the service environment.
If your load-bearing application runs dry (indoor electronics enclosures, automotive under-hood with proper sealing), nylon is excellent. If it sees outdoor humidity or washdown conditions, you need a moisture-stabilized grade or you need to look at PC instead.
Impact warning. Here’s where nylon falls down. Notched Izod for PA66 is 60-100 J/m. PC is 600-900 J/m. That’s not a small difference — that’s an order of magnitude. If your part sees repeated impact loading — a latch that slams shut, a tool housing that gets dropped — nylon can crack through before you’ve hit 10,000 cycles. Glass-filled nylon improves stiffness and tensile but makes impact even worse.
PC: The Impact King
Polycarbonate’s party trick is impact resistance. 600-900 J/m notched Izod is absurdly high for an engineering thermoplastic. Drop a PC housing from waist height onto concrete and it bounces. Drop ABS and it might crack. Drop nylon and it almost certainly cracks.
But it creeps. PC’s tensile strength is 60-70 MPa — respectable. Its creep at 50% load over 1000 hours is 0.8%, comparable to PA66 dry. The catch is time. Under continuous load, PC’s creep rate accelerates past the 10,000-hour mark in ways nylon’s doesn’t. For a part that carries load for years — not months — PC can surprise you with permanent deformation.
Chemical sensitivity. PC stress-cracks in the presence of hydrocarbons, greases, and even some cleaning solvents. That automotive bracket that sees occasional oil mist? PC might fail within weeks. That power tool housing that gets wiped down with isopropyl alcohol? PC will craze before your eyes.
PC is the right choice when impact is the primary threat and the load is intermittent or well-supported — snap-fit housings, consumer electronics enclosures, face shields. It’s the wrong choice when the load is continuous and the environment is chemically aggressive.
ABS: The Practical Choice
ABS doesn’t dominate any single metric. That’s fine — it dominates on value.
At 1.0x cost index (baseline), ABS gives you 40-50 MPa tensile strength, 150-350 J/m impact resistance, and excellent surface finish. Unless you need extreme performance in any one direction, it works.
Where ABS surprises. Plating-grade ABS can be chrome-plated or painted. That opens up cosmetic and corrosion-resistance options that PC and nylon don’t offer as easily. For decorative housings with functional loads — think medical device enclosures, appliance panels, consumer electronics — ABS is often the most economical path to a production-ready part.
The limits. 1.2% creep at 50% load over 1000 hours is the worst of the three. If your part sees a constant load, ABS will deform faster than PC or nylon. Its max service temperature is about 80°C — above that, the material softens noticeably. And while 150-350 J/m impact is decent, it’s nowhere near PC’s headroom.
ABS is your daily driver. It handles most jobs competently and cheaply. But when you push it — high load, high temperature, repeated impact — it shows its limits.
When to Choose Which
| Application | Best Pick | Why |
|---|---|---|
| Structural bracket, sustained load, dry environment | PA66 | Best tensile + creep resistance |
| Structural bracket, sustained load, humid environment | PC | Dimensional stability in moisture |
| Power tool housing, repeated drops | PC | 600-900 J/m impact absorbs drops |
| Decorative enclosure, light load, any volume | ABS | Best surface finish, lowest cost |
| Gear or pulley, dry, high wear | PA66 | Flexural modulus + wear resistance |
| Snap-fit housing, frequent assembly/disassembly | PC | Fatigue life beats nylon and ABS |
| Automotive under-hood, chemical exposure | PA66 (stabilized) | Chemical resistance where PC fails |
The Verdict
There is no universal winner. Here’s my rule of thumb from twenty years on the press:
- Load is the primary threat — start with nylon (PA66 if you can afford it, PA6 if cost matters)
- Impact is the primary threat — start with PC
- Cost is the primary constraint and loads are light — start with ABS
- You need both load and impact — PC/ABS blend or glass-filled nylon with impact modifier
That last one is worth repeating. When you genuinely need both high tensile strength and high impact resistance, a single material won’t cut it. PC/ABS blends give you a middle ground — 55-65 MPa tensile, 400-600 J/m impact. Or go with impact-modified, glass-reinforced PA66 and accept the mold wear that comes with glass content.
I’ve helped engineering teams work through this decision on hundreds of projects. There’s no magic bullet — just honest tradeoffs and good data. If you’ve got a part that needs to carry load and take hits, send us your design. We’ll run the FEA, check the service conditions, and recommend the right material before we cut any steel.