Plastic Resin 101: A Materials Guide for Custom Injection Molding

Choosing the right plastic resin can make or break a project. It affects how a part performs, how long it lasts, and how much it costs to produce. At Metro Plastics, we work with a range of engineering-grade thermoplastic resins, and each one brings something different to the table. Whether you’re designing a part for industrial equipment, agriculture, electronics, or food and beverage applications, understanding your material options is the first step toward a successful custom injection molding project.

This guide breaks down the plastic resins we use most often, what they’re good for, and how to think about material selection for your next part.

What Is Plastic Resin, Anyway?

Before it becomes a finished part, plastic starts out as resin, small pellets that get heated, injected into a mold, and cooled into shape. Different resins have different molecular structures, and that structure determines how the material behaves. Some resins flex easily and resist impact. Others hold tight tolerances and stand up to heat. Picking the wrong one can mean a part that warps, cracks, or simply doesn’t perform the way it needs to.

That’s why plastic resin selection isn’t something to guess at. It’s a decision that should factor in the part’s function, its environment, and the industry it’s built for.

ABS: The Reliable, Everyday Plastic Resin

ABS (Acrylonitrile Butadiene Styrene) is one of the most widely used resins in injection molding, and for good reason. It’s tough, dimensionally stable, and relatively easy to mold into complex shapes. ABS holds up well to everyday wear and impact, which makes it a go-to choice for housings, enclosures, knobs, and structural components across consumer goods, appliances, and lawn and garden equipment.

If a part needs to be durable without requiring extreme heat or chemical resistance, ABS is often the most cost-effective plastic resin for the job.

Polycarbonate (PC): Built for Strength and Clarity

Polycarbonate steps in when a part needs more than ABS can offer. PC resin is known for exceptional impact strength and heat resistance, and it can be molded into optically clear components when needed. That combination makes it a strong fit for electrical housings, safety guards, lenses, and components used in food and beverage equipment where durability and cleanliness both matter.

Because PC has a low shrink rate, it also holds tighter tolerances than many other resins, which is valuable for parts with precise fit requirements.

Nylon: The Wear-Resistant Workhorse

Nylon (polyamide) is the resin of choice when a part needs to withstand friction, wear, or repeated mechanical stress. It’s commonly used for gears, bushings, fasteners, and other components that move against other surfaces. Nylon’s chemical resistance also makes it a strong option for agriculture and industrial equipment, where parts are regularly exposed to oils, fuels, or outdoor conditions.

One thing to plan for with nylon is its higher shrink rate compared to resins like PC. Our engineering team accounts for this during mold design so the finished part still meets dimensional requirements.

ABS/PC Blends: The Best of Both Worlds

Sometimes a project calls for a balance that a single resin can’t quite deliver. ABS/PC blends combine the impact resistance and heat tolerance of polycarbonate with the easier moldability and cost efficiency of ABS. This makes the blend a popular option for housings and covers in electronics and industrial applications where performance and manufacturability both matter.

How Metro Plastics Helps You Choose the Right Plastic Resin

Material selection isn’t something we hand off to a catalog. Our engineering team has more than 100 years of combined experience, and part of that expertise is knowing how a specific resin will behave in your application, your mold, and your production environment. When you bring us a project, whether it’s a prototype, a transfer tooling job, or a full production run, we’ll walk through the best materials and processes for your part, factoring in performance requirements, tolerances, industry standards, and cost. You don’t have to arrive with the material already decided. That’s part of what we’re here for.

Plastic Resin Selection Is Just the Start

Picking the right plastic resin is one piece of a much bigger process. From there, our team considers mold design, tooling, insert molding needs, and value-added services like in-mold labeling or custom automation. Metro Plastics has spent 50 years building the kind of relationships and expertise that make custom injection molding projects run smoothly from concept to creation.

If you’re not sure which plastic resin fits your project, that’s a conversation worth having early. Contact Metro Plastics today, and let our team help you find the right material for the job.