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In a basic plastic extruding process, plastic is first melted into a viscous, semi-liquid state. After it softens, the plastic is pressed through a contoured opening. The plastic ooze emerges from the opening in a long shape with the same cross section as the opening. This shape can be cut to any length necessary, allowing for a great number of possible components.

Plastic extrusions are normally manufactured with thermoplastics, although thermoset plastics can also be extruded. Some of the materials regularly extruded are polytetrafluoroethylene (PTFE), polyurethane, nylon, vinyl and acrylic, among many others. Perhaps the most advantageous aspect of plastic extrusion is its low cost, which is virtually unsurpassed by any other plastic processing operation. Plastic extruding is also a highly efficient process, as it is a continuous operation that generates little wasted material. This is in contrast to injection molding, which encounters numerous changes while the melt is sent into the mold, and which involves higher pressures. In addition, the rotating screw central to any extruding system melts, mixes and drives the plastic through the opening, thereby economizing size and machine cost.

Plastic extrusion is used to create a wide range of items, including plastic tubing, trims and seals, and plastic sheets and rods. There are a number of extrusion techniques available to manufacturers, such as co-extrusion, offset extrusion, oriented extrusion, overcoat extrusion, cold extrusion, ram extrusion and much more. Screw extrusion machines are used in the manufacture of the vast majority of extruded thermoplastics. The ram extrusion process is effective for certain specific materials, such as PTFE resin, that cannot be successfully processed by a screw extruder. Co-extrusion is useful when manufacturing products with wedded components that have distinctly different attributes. This might include a hard plastic tube with a softer exterior, or a plastic facing with a spongy plastic backing.

Screw extruders can involve a single screw or multiple screws, each of which has benefits and drawbacks. One drawback to most extrusion operations is that dimensional tolerances are relatively high, ranging up to 10% of the work piece. This varies based on the material used, as well as the specifics of the process in question (temperature, post extrusion techniques, etc.). In general, literature recommends precision controlled down-system equipment, precise and continuous flow rates, and uniformity of melt-heat profile and mix.