Contact Us

What’s the Difference Between Rotational Molding and Injection Moulding?

Colorful slides made with rotational molding

In the vast world of plastic manufacturing, the choices you make regarding the production process can significantly impact the end product’s quality, cost, and versatility. Two processes stand out in particular: Rotational Molding and Injection Moulding.

But which one should you choose for your next project? In this comprehensive breakdown, we’ll examine the differences between these two methods and explain why rotational molding may offer the edge you need to create superior plastic products.

Understanding Rotational Molding

Rotational Molding, sometimes known as rotomolding, is a plastic molding process ideal for producing large, hollow plastic parts. The process begins with a closed mold filled with a predetermined amount of plastic powder resin. It is then heated, usually in an oven, causing the mold to rotate on two perpendicular axes, spreading the resin over the surface of the mold. After cooling, the part is removed, resulting in a seamless, one-piece, hollow object.

This method is best suited for parts that would be costly or impossible to produce by any other method due to the depth and complexity of the shapes. The hollow portions of the part can be filled with foam for additional structural integrity and insulation, making final products highly versatile for every industry where they apply.

The Unique Benefits of Rotational Molding

Here are the key advantages of Rotational Molding:

Ideal for Larger Parts: Rotational molding can handle much larger parts than injection molding. The larger capacity of rotational molds allows for the production of big parts like storage tanks, playground equipment, and furniture.

High Strength & Durability: Because the process involves uniform material distribution, products made through rotational molding tend to be robust. They can withstand the test of time, even in harsh environments.

Cost-Effective Tooling: Molds for rotational molding are typically less expensive, making them cost-effective for smaller production runs and prototypes. The molds used are durable, which helps lower costs across the board.

Design Flexibility: This method allows for greater design freedom, enabling you to integrate complex shapes and undercuts without incurring additional tooling costs.

Injection Molding vs. Rotational Molding: Which One Fits Your Project?

Here’s a comparison between Injection Molding and Rotational Molding processes to help you make an informed choice:

Part Size & Complexity: While Injection Moulding is efficient for smaller, intricate parts, Rotational Molding’s strength lies in handling large, complex shapes with ease.

Material Options: Injection Moulding supports a broader range of materials, including engineering-grade plastics. However, regarding durability, rotational molding often uses a wider variety of plastics and plastic types, such as LDPE, HDPE, PP, and PVC.

Production Speed & Volume: Injection Moulding is a faster process and is better suited to high-volume production. On the other hand, Rotational Moulding is better for custom and lower-volume production.

Typical Applications: There’s a significant overlap in applications, but Rotational Molding is often favoured for products like agricultural tanks, fuel tanks, and custom cases—items that demand resilience and size.

When to Choose Rotational Molding

Choosing Rotational Molding as your production technique makes a lot of sense when your project involves creating large, hollow products that need to be incredibly durable. Think about items that will be used outdoors, like kayaks, coolers, or large storage bins. These products benefit from the seamless construction and uniform wall thickness that rotational molding offers, resulting in items that can handle a lot of wear and tear. It’s also a great choice if you’re making a limited number of items because it won’t cost you as much to get started with the molds. If your project fits this description, then rotational molding might just be the perfect match for your needs.


Rotational Molding’s capability to produce large, durable parts economically without undermining design flexibility is a compelling reason to consider it for your next project. It’s a process that marries cost efficiencies with high-quality outcomes for applications ranging from medical equipment to recreational vehicles.

Are you interested in exploring how Rotational Molding could elevate your product line? Contact us for a consultation on how this versatile manufacturing process can be tailored to meet your specific needs.

Frequently Asked Questions About Rotational Molding

Q: Which industries can benefit the most from Rotational Molding?

A: Rotational Molding is incredibly versatile and can benefit numerous industries requiring durable, large, and complex plastic parts. Key industries include automotive manufacturing parts like fuel tanks, agriculture for creating large water and feed tanks, recreation for producing items such as kayaks and playground equipment, and industrial sectors for storage bins and safety equipment. It’s also widely used in various applications in the construction, marine, and healthcare industries.

Q: Are there any limitations to the size of products that can be created with Rotational Molding?

A: While Rotational Molding is renowned for its ability to produce very large plastic parts, there are practical limits to the size of products it can create, primarily determined by the size of the machine. The largest rotational molds can produce items up to several meters in length, width, or height, but each machine has its maximum capacity. Transportation and handling extremely large molds and finished parts can also present logistical challenges.

Q: How does the cost of Rotational Molding compare to other plastic manufacturing processes?

A: Generally, Rotational Molding is more cost-effective for small to medium production runs due to lower mold and setup costs compared to processes like Injection Molding. However, the per-unit cost can be higher than alternative methods for very high-volume production. The process’s cost-efficiency is especially notable in producing large, complex parts and items with specific requirements such as thickness and durability.

Q: Can rotational molding be used to produce multi-layered parts?

A: Yes, one of the unique capabilities of Rotational Molding is producing parts with multiple layers of plastic. This is particularly valuable for products requiring different properties on the inside and outside layers, such as fuel tanks with a barrier layer or parts that need a high-quality aesthetic exterior with a different interior material. This multi-layer process adds to the method’s flexibility and the range of products it can create.

SPI Plastics Inc.

165 Stoneman Drive, Box 100
(Shouldice Block Road & Joynt Street)
Shallow Lake, ON
N0H 2K0

T   519-935-2211
TF 800-269-6533
F   519-935-2174

Business Hours

Monday - Thursday: 8am to 4:30pm
Friday: 8am to 4pm
Saturday & Sunday: Closed

Find Out More About SPI Plastics Inc.

Learn More

Contact SPI Plastics