• Shorter cycle time: No runner controlling the cooling time
• Easier to start: Without runners to remove, and auto cycle occurs faster and more frequently
• Fewer sink marks and under-filled parts: Unlike when plastic flows through a cold runner and loses heat to mold plates
• Design flexibility: Can locate the gate at many points on the part
• Balanced melt flow: Separate melt channels are in externally heated manifolds that are insulated from mold plates surrounding them.^[1]

Hot runner systems were first developed and came into sporadic use in the early 60s with generally negative results. They gained popularity in the 80s and 90s as technological advancements allowed improved reliability and the escalation of plastic materials prices made hot runner systems more desirable and cost effective. Hot runners are fairly complicated systems, they have to maintain the plastic material within them heated uniformly, while the rest of the injection mold is being cooled in order to solidify the product quickly. For this reason they are usually assembled from components pre manufactured by specialized companies.

A hot runner controller is a temperature controller used to control the temperature in the hot runner. This helps create the most consistent part(s).

Hot runners usually make the mold more expensive to manufacture and run, but allow savings by reducing plastic waste and by reducing the cycle time. (do not have to wait until the conventional runners freeze).