What is the difference between injection blow molding and extrusion blow molding?

Blow molding is used to make thin-walled containers such as balloons and bottles. There are two types of blow molding processes:

Extrusion blow molding:

This is the more popular choice in blow molding. Plastic pellets are fed from a hopper into an extruder, which uses friction to heat the plastic into a liquified state. The molten plastic is extruded into a hollow tube, called a parison. Pressurized air is then blown into the parison, forming it into shape. Excess plastic on the bottom of the container is trimmed. Containers are then sent to a second trimming station, where the top is trimmed. When possible, this excess is recycled back through the process to limit waste.

Injection blow molding:

Injection blow molding creates greater detail than extrusion blow molding. Resin pellets are fed from a hopper into an extruder. The pellets are then melted and injected into a preform mold around a core rod. Pressurized air is blown into the mold, forcing the plastic to take shape.

The final step in both molding processes is to check for leaks. If a leak is detected the container is recycled back into production to limit waste.