Injection Molding vs Rotational Molding – What You Need to Know Before You Buy

Kayaker paddling in a rotomolded kayak

Regardless of the products you’re purchasing—from plastic kayaks and playground equipment to poly dumpsters and traffic cones—you’re making an investment in equipment. Equipment you’re counting on to last. So, as you’re narrowing your options with ROI in mind, it’s critical that you weigh the benefits of plastic injection molding vs rotational molding (or rotomolding) manufacturing processes against each other.

Let’s take a look.

What is rotomolding?

When you think rotational molding, think layers.

When manufacturing a poly-based product using a rotational molding process, the virgin material and powdered colorant are poured into the mold. The mold is then bolted tight, placed in an oven, and rotated at an even speed. In this way, the plastic is laid down in thin layers of even thickness, regardless of whether or not the mold features corners and curves.

After the material is baked, the plastic is cooled inside the mold, ensuring it hardens evenly, and then extracted.

How does the injection molding process differ?

When manufacturing injection mold products, the material is melted and slowly forced into a stationary mold under high pressure. This process then utilizes pressure to distribute the material throughout the mold, ensuring coverage of the mold’s entire shape.

When complete, the two molds are pulled apart, and the plastic is removed and cooled.

Injection molding vs rotational molding: Which process wins?

The plastic rotomolding process offers some distinct advantages when it comes to commercial and industrial applications.

We manufacture plastic dumpsters and residential carts for the waste industry, for example. And, these products take their fair share of abuse. Not only that, they may be exposed to extreme temperatures, as well.

blue front-load plastic dumpster

Because rotational molding produces a more even application of the plastic material, the resulting product is more flexible and durable. Meaning, it’s less likely to crack in extreme temperatures or when beaten up by waste handlers on their runs.

You just can’t achieve a consistent wall thickness with injection molding.

These plastic injection mold products will be thinner in the corners, and they can’t offer the same degree of material flexibility. Meaning, they’re less forgiving of daily abuse—and more likely to fail in Arizona summers and North Dakota winters.

Why do some manufacturers produce injection mold products?

Injection molding comes with some serious drawbacks, but the process isn’t without its benefits.

This manufacturing process can support more complex mold designs (think little green army men), as well as a broader range of materials. Manufacturers can also turn out more items on the production line using this process, reducing their production costs.

An injection molded Army man. Tough, but not so tough.

Choosing the right plastic products for your application

In our industry, poly-based products—plastic dumpsters and residential carts—are beaten up and abused. Businesses and homeowners may dump corrosive materials, garbage handlers may beat up on the equipment, and both massive temperature swings and climate extremes put the poly material to the test.

Some industries and applications, however, demand less durability from their plastic products. In those cases, the weak points and potential for injection mold defects present less risk.

So consider the demands you’ll place on your plastic products. If they’ll be used and abused, we highly recommend you consider rotational mold products. They’re simply higher-quality and more durable than their injection mold counterparts—delivering you greater ROI.

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