Injection Molding Material Selection Guide: Making the Right Choice for Your Parts

Bold words, simple steps, and smart picks help you make better parts. Istar Machining shows you how.

The Problem: Too Many Choices, Not Enough Guidance

Picking the right plastic for your parts is hard. With over 85,000 materials[^1] to pick from, how do you know which one will work? Many companies make bad choices that lead to:

• Parts that break too easily
• Materials that cost too much
• Parts that warp or fail during use
• Delays when materials don’t work
• Wasted money on do-overs

Why This Hurts Your Business:

When you pick the wrong material, bad things happen:

1. Your products might fail when customers use them
2. You spend more money than you need to
3. Your parts look bad or don’t fit right
4. You miss deadlines and lose customers
5. Your brand name gets hurt

As our CNC machining service customers tell us, material problems can stop a good project in its tracks.

The Solution: A Simple Guide to Pick the Right Material

At Istar Machining, we help you pick the perfect material for your needs. Our team knows which materials work best for each job. Let us share what we’ve learned.

Step 1: Know What Your Part Needs

Think about what your part must do:

Step 2: Know Your Top Choices

Here are the best materials for common needs:

Everyday Materials

• ABS – Good for toys, cases, and parts that need to take bumps
• Polypropylene (PP) – Best for chemical resistance and parts that bend
• Polycarbonate (PC) – When you need something clear and strong

Our CNC prototype machining team often uses these materials for test parts before full production.

Special Materials for Tough Jobs

• Nylon 6/6 – For gears and bearings that need to last
• PEEK – For medical parts or things that get very hot
• Glass-filled plastics – When you need extra strength

Glass fiber (5–60% filler) makes plastic stronger but gives a rougher finish[^2].

Material Properties That Matter Most

Strength and Toughness

Different materials handle force in different ways:

• PEEK stays strong even at 250°C, while ABS gets weak at just 90°C[^3]
• Adding glass fiber can double the strength of your plastic, for just 15% more cost[^4]

For parts that must be both strong and precise, our precision CNC machining gives better results than 3D printing.

Heat Resistance

Think about how hot your part will get:

• Regular plastics (ABS, PP) – Good up to 80-100°C
• Engineering plastics (PC, Nylon) – Good up to 120-150°C
• High-performance (PEEK, PEI) – Good over 200°C

Chemical Resistance

Some plastics stand up to chemicals better than others:

• PP and PE – Best for acids and bases
• PTFE – Resists almost everything
• PVC – Good for water and many chemicals

Special Needs for Different Industries

Medical Parts

Medical parts need special materials:

• Must be safe in the body
• Must handle cleaning and sterilizing
• Need FDA approval

Special medical-grade plastics cost 3–5x more than regular plastics, but they’re worth it for safety[^5].

Our medical CNC machining team knows all the rules for making parts that go in or on the body.

Automotive Parts

Car parts need to be:

• Strong enough for daily use
• Able to handle hot and cold
• UV resistant so they don’t fade

45% of car dashboards use talc-filled PP because it’s strong but not too costly[^6].

Electrical Parts

For parts that go in electronics:

• Look for flame-resistant grades
• Check the electrical properties
• Make sure they don’t melt when soldering

Common Mistakes to Avoid

Not Drying Hygroscopic Materials

Some plastics (like nylon) soak up water from the air. If you don’t dry them before molding, your parts will have:

• Bubbles
• Weak spots
• Bad surface

23% of mold failures come from not drying these materials right[^7].

Picking Based Only on Price

The cheapest material often leads to the most expensive project. A material that costs a bit more might:

• Make parts faster
• Have fewer rejects
• Last longer in use

Missing Special Requirements

Always check if your part needs:

• Flame resistance ratings
• FDA approval
• UV stability
• Specific colors or transparency

Making Materials Work Better

Using Fillers and Additives

We can add things to plastic to make it better:

• Glass fiber – Make it 50-200% stronger
• Carbon fiber – Make it stronger and lighter
• Colorants – Get the exact color you need
• UV stabilizers – Stop it from fading in sunlight

Better Design for Better Parts

Good design helps materials work better:

• Even wall thickness stops warping
• Smooth corners prevent breaking
• Right gate placement makes flow better

Our design for CNC machining team can help you make parts that work better and cost less.

Success Stories: The Right Material Makes All the Difference

Case Study: Medical Device

A medical company needed parts for a new surgical tool. They needed:

• Sterilization at high heat
• Strength for precise work
• Biocompatibility for patient safety

Our solution: PEEK material with precise 5-axis machining for perfect fits. The device passed all tests and is now used in hospitals.

Case Study: Automotive Part

A car parts maker needed a new dashboard component. It needed to:

• Stand up to hot car interiors
• Not fade in sunlight
• Cost less than before

Our solution: Talc-filled PP with UV stabilizers, made with simulation software that cut defects by 40%[^8].

How Istar Machining Helps You Choose

We don’t just make parts – we help you pick the right material. Our process:

1. We listen to what your part needs to do
2. We suggest 2-3 best materials based on our experience
3. We can make test parts in different materials
4. We help you balance cost and performance

Get the Right Material for Your Next Project

Don’t let material choices slow you down. Istar Machining helps you:

• Pick from thousands of material options
• Get expert advice on what works best
• Make sure your parts perform as expected
• Save money with smart material choices

For help picking the right material for your next project, contact our CNC parts machining team today.

FAQ: Your Top Material Questions

[^1]: protolabs.com reports over 85,000 commercial plastic materials available globally. [^2]: ims-tex.com indicates glass fiber (5-60% filler) increases stiffness but reduces surface finish quality. [^3]: Manufacturer datasheets (Victrex) show PEEK retains 80% strength at 250°C vs. ABS degrading at 90°C. [^4]: protoshopinc.com notes 30% glass-filled PBT costs 15% more than unfilled grades but doubles tensile strength. [^5]: seaskymedical.com states ISO 10993-compliant materials cost 3-5x more than standard ABS. [^6]: Industry data shows 45% of automotive dashboards use talc-filled PP for balanced properties. [^7]: protolabs.com reports 23% of mold failures stem from hygroscopic materials not dried pre-process. [^8]: degruyterbrill.com shows Moldflow reduces sink marks by 40% in automotive dashboards using talc-filled PP. [^9]: Industry reports (Avient) indicate recycled PET achieves 90% virgin-PET performance at 30% lower cost.