What is Plastic?

What is Plastic?
article writer
by Keith McCauley
September 8, 2020, Updated October 28, 2022

An imagination is a terrible thing to waste. Children don't question Dr. Seuss' far-fetched, never-ending pipe mazes for plausibility. They merely accept the fact that ingredients go in one end and a finished product comes out the other. The creation and subsequent lifecycle of plastics follows a similar model. The twists, turns and roundabouts may not actually exist, but for entertainment value and the sake of the inner-child within each of us, come explore the lively process of packaging production.

Polyethylene Terephthalate

Polyethylene Terephthalate, also known as PET, is a member of the polyester family. Made from carbon, hydrogen and oxygen, the strong and naturally colorless resin is lightweight and ranges from semi-rigid to rigid flexibility. Packaging made from this material will sport the #1 resin identification code. Most common uses include beverage and food containers.

High Density Polyethylene

High Density Polyethylene, often referred to as HDPE, is built from carbon and hydrogen elements. This plastic is hard, opaque in color and is adorned with the #2 resin identification code. Its many packaging applications range from milk jugs, laundry and dish detergent containers to bleach and lotion bottles.

Polyvinyl Chloride

Made from carbon, chlorine and hydrogen, this plastic is durable and chemically resistant. Marked with resin identification code #3, its most common uses include shampoo bottles as well as oil and chemical containers.

Low Density Polyethylene

Built from carbon and hydrogen, low density polyethylene (LDPE) is marked with resin identification code #4 and has a high heat tolerance. Its appearance varies from translucent to opaque. This material is often used to form storage containers, produce bags and squeezable containers.


Created from carbon and hydrogen, polypropylene (PP) is a stiff plastic marked by resin identification code #5. This material has a high heat tolerance and can be translucent, opaque or colorful. Most common polypropylene items include bottle caps, cereal box liners and drinking straws.


Built from carbon and hydrogen, this extremely rigid plastic is set apart by the resin identification code #6. It can be presented in transparent or colorful varieties. Common items made from this material include yogurt cups, carryout containers, disposable cutlery as well as meat and produce trays.

Now you know what each plastic is really made of (all the way down to its elemental origins)! Some containers can be fluorinated while others are flame treated. Some are formed through extrusion blow molding while other take shape through injection molding. Continue to follow the swooping pipes of our infographic to become more familiar with and learn the details behind each resin type.



  • There are 7 categories of plastic resins. This infographic does not include the 7th resin type OTHER because this category is the catch-all category. There are thousands of types of plastics marked with a 7 that have different ingredients and molding processes.
  • Phthalates are plastic additives that make plastic flexible. Orhthopthalates, a sub category of phthalates, have been discontinued in food-contact PVC in Europe and North America due to potential health risks.
  • HDPE and LDPE containers are typically flame treated or flourinated in after-market settings. Please contact us if you require flame treating or fluorination.