Plastic Injection Molding Machine in a Factory

Hot Runner Systems Versus Cold Runner Systems

In plastic injection molding, there are two primary ways to categorize injection molds: hot runner and cold runner. 

Each “system” has its advantages and disadvantages. Ultimately, choosing between these two systems comes down to cost limitations, part size, and the application itself. 

In this article, we’ll discuss the primary differences between hot runner systems and cold runner systems and how to pick the right system for your application. 

Hot Runner Systems

There are two primary categories of hot runner molds: externally heated and internally heated. As both names suggest, externally heated molds are heated by an external element, while internally heated molds are heated internally.

In both externally and internally heated systems, the plastic resin remains molten throughout the entire plastic injection molding process. And once the molded part or substrate is ejected from the mold’s cavity, there is zero plastic residue inside the channels.


  • Low Waste
  • High Cycle Times
  • Excellent Processing
  • Uniform Heat Distribution (Mold)


  • High Initial Cost for the Mold
  • Mold Requires Consistent Maintenance
  • Can’t Run Certain Resins With Low Melting Points
  • Changing Resin Colors is More Difficult

When to Use a Hot Runner System

Hot runners are better suited for the mass production of plastic components. They’re also ideal for applications that have complex designs or require multiple cavities. 

Cold Runner Systems

In a cold runner system, molten plastic is injected into the mold, which flows through the runners into the mold’s cavity. Unlike hot runner systems, cold runner systems don’t externally or internally heat the resin as it flows through the mold. In a cold runner system, the molten plastic cools as it runs through the system. Once the part is ejected from the mold, the plastic runners and gates must be manually removed from the plastic molded part. While some runners and gates can be reground or recycled, cold runners still produce more waste than hot runners.


  • Less Expensive Upfront
  • Lower Maintenance Costs
  • Changing Resin Color Is Easier
  • Works Well With Temperature/Heat-Sensitive Resins


  • Low Cycle Times
  • Generates More Waste
  • Plastic Runners & Gates Must Be Manually Removed

When to Use a Cold Runner System

Cold runner systems are ideal for producing plastic components with simpler designs. They’re also widely used when cost is an important factor, as cold runner systems do not have as many overhead costs as hot runner systems. Cold runner systems also provide more versatility, as a wide range of heat-sensitive resins work well within this system.

Learn More From Silver Basis Engineering

Silver Basis Engineering is an award-winning global manufacturing provider specializing in plastic injection molding and semi-solid die casting. We design and produce parts for clients in all industries, including automotive, aerospace, defense, and medical. Please visit our blog today for more plastic injection molding resources, or contact us today to learn more about our capabilities.