What Is the Strength of the 7 Most Common Injection Molding Plastics

 

Why “Strength” Isn’t Just About Tensile Numbers

Before we dive into materials, let’s clarify what “strength” really means in practice:

• Tensile strength: Resistance to pulling forces (e.g., a handle being lifted).
• Impact strength: Ability to absorb sudden shock (e.g., a crate dropped from height).
• Flexural strength: Resistance to bending (e.g., a chair leg under load).
• Creep resistance: Performance under long-term stress (e.g., a bracket holding weight for years).
• Environmental resistance: How UV, moisture, heat, or chemicals affect performance over time.

A plastic might score high in one area but fail in another. The key is fit-for-purpose strength—and that’s where material selection becomes a strategic decision.

 

1. Polypropylene (PP) – The Resilient Everyday Performer

• Tensile Strength: 30–40 MPa
• Impact Strength: Moderate (improves with copolymer variants)
• Key Strengths: Excellent fatigue resistance, chemical inertness, low moisture absorption
• Typical HOPO Applications: Dustbin moulds, bucket moulds, crate boxes, washing machine inner tubs

PP may not win a strength contest on paper, but it’s a hero of real-world durability. It flexes without cracking—perfect for living hinges, snap-fit lids, and containers that endure daily drops and outdoor exposure. UV-stabilized PP even holds up for years in sunlight.

At HOPO, we often recommend homopolymer PP for rigidity and copolymer PP for impact-critical parts—tailoring the grade to your use case.

 

2. Acrylonitrile Butadiene Styrene (ABS) – The All-Rounder with a Polished Finish

• Tensile Strength: 40–55 MPa
• Impact Strength: High (thanks to butadiene rubber phase)
• Key Strengths: Good rigidity, excellent surface finish, easy to paint or plate
• Typical HOPO Applications: Air conditioner housings, refrigerator liners, power tool casings

ABS strikes a rare balance: structural integrity + aesthetic quality. It’s strong enough for appliance shells that must support weight and vibration, yet smooth enough for visible surfaces. It’s also easy to mould consistently—making it a favorite for high-volume production.

Note: ABS isn’t UV-stable—so it’s best kept indoors or protected with coatings for outdoor use.

 

3. Polycarbonate (PC) & PC Blends – The Impact Champions

• Tensile Strength: 55–75 MPa
• Impact Strength: Exceptional (among the highest of all thermoplastants)
• Key Strengths: Transparency (in pure PC), high heat deflection, low-temperature toughness
• Typical HOPO Applications: Safety guards, transparent appliance windows, automotive interior panels (often as PC/ABS)

Pure PC is used where safety and clarity matter—like riot shields or medical device housings. But for most consumer and industrial parts, PC/ABS blends are smarter: they retain ~80% of PC’s impact strength while gaining ABS’s flowability and lower cost.

At HOPO, we ensure PC resins are thoroughly dried before moulding—moisture causes hydrolysis, leading to brittleness and cosmetic defects.

 

4. Polyamide (Nylon – PA6 / PA66) – The High-Stress Workhorse

• Tensile Strength:
  • Unfilled: 70–85 MPa
  • 30% Glass-Filled: 120–180 MPa
• Impact Strength: Good (unfilled); reduced but stiffer when filled
• Key Strengths: High abrasion resistance, good performance at elevated temps
• Typical HOPO Applications: Automotive air ducts, fan blades, industrial gears, structural brackets

Nylon’s real power shines when reinforced. 30% glass-filled PA66 is a staple in under-hood automotive parts because it handles heat, oil, and vibration without deforming. But it’s hygroscopic—so parts may swell slightly in humid environments.

Our mould designs account for anisotropic shrinkage in glass-filled nylon—preventing warpage through optimized cooling and gate placement.

 

5. Polyoxymethylene (POM / Acetal) – The Precision Powerhouse

• Tensile Strength: 60–70 MPa
• Impact Strength: Moderate to good
• Key Strengths: Extremely low friction, high fatigue endurance, exceptional dimensional stability
• Typical HOPO Applications: Gears, latches, drawer slides, fluid connectors, chair mechanisms

POM won’t win on tensile strength, but it dominates in dynamic, moving parts. It “clicks” reliably, wears slowly, and holds tight tolerances—even after millions of cycles. That’s why it’s the go-to for precision mechanical components.

Important: POM releases formaldehyde when processed. Our moulds include enhanced venting systems to ensure safe, clean production.

 

6. High-Density Polyethylene (HDPE) – Toughness Through Simplicity

• Tensile Strength: 20–30 MPa
• Impact Strength: Very high (especially at low temps)
• Key Strengths: Outstanding chemical resistance, excellent stress-crack resistance, easy to process
• Typical HOPO Applications: Chemical tanks, outdoor bins, bottle caps, storage containers

HDPE proves that low tensile strength doesn’t mean weak performance. Its molecular structure resists cracking under constant stress—making it ideal for containers holding detergents, fuels, or water for years. It’s also fully recyclable and cost-effective.

We often pair HDPE with UV inhibitors for outdoor dustbins or agricultural crates to prevent embrittlement.

 

7. Polybutylene Terephthalate (PBT) – The Quiet High Performer

• Tensile Strength:
  • Unfilled: 50 MPa
  • 30% Glass-Filled: 140–170 MPa
• Impact Strength: Moderate (improved with elastomer modification)
• Key Strengths: Fast cycle times, excellent electrical insulation, flame-retardant grades available
• Typical HOPO Applications: Electrical connectors, automotive sensor housings, appliance switch components

PBT is often overlooked—but it’s a star in electrical and automotive miniaturization. It flows well into thin walls, resists tracking, and maintains shape at 130–150°C. Flame-retardant PBT is UL94 V-0 rated—critical for safety-certified parts.

Due to its fast crystallization, PBT moulds require precise temperature control—a standard capability in HOPO’s tooling process.

 

How Material Strength Directly Impacts Your Mould Design

Choosing a plastic isn’t just about the part—it shapes the entire mould:

• Glass-filled materials (like GF-PA66 or GF-PBT) are abrasive—requiring hardened H13 or stainless steel cavities.
• High-shrinkage resins (PP, HDPE, POM) demand accurate shrinkage compensation in cavity design.
• High-temp plastics need efficient cooling channels to control cycle time and warpage.
• Low-viscosity materials (like HDPE) require tight parting lines to prevent flash.

At HOPO Mould, we run mould flow simulations (Moldex3D) on every project to predict how your chosen material will fill, pack, and cool—ensuring mechanical performance isn’t compromised by hidden defects like weld lines or voids.

 

So, Which Material Gives You the “Right” Strength?

Ask yourself:

Application	Recommended Material
Outdoor dustbin or crate	UV-stabilized HDPE or PP
Washing machine drum	Copolymer PP or ABS
Air conditioner housing	ABS or PC/ABS
Automotive structural bracket	30% GF PA66 or PBT
Precision gear or latch	POM (Acetal)
Electrical connector	Flame-retardant PBT
Transparent safety cover	Polycarbonate (PC)

Strength is contextual. The goal isn’t to pick the strongest plastic on Earth—it’s to select the most reliable, cost-effective, and manufacturable material for your specific need.

 

Partner with HOPO for Smarter Material-to-Mould Decisions

Located in Huangyan, Taizhou—the heart of China’s mould industry—HOPO Mould combines deep engineering experience with modern tooling capabilities. Since 2012, we’ve delivered high-precision moulds for:

• Home appliances: AC, washing machine, refrigerator
• Daily commodities: dustbin, bucket, chair, crate box
• Automotive & industrial: connectors, ducts, fittings

With 40-minute access to Taizhou Airport and 15 minutes to the railway station, we offer global clients fast, reliable service without compromising quality.

Got a new part in development? Share your function, environment, and volume—and we’ll help you choose the right material and build the perfect mould for it.