Most plastic is made from fossil fuels, specifically crude oil and natural gas. These raw materials supply the carbon-rich molecules that get transformed through heat and chemistry into the polymers found in everything from water bottles to car bumpers. The world used roughly 464 million metric tons of plastic in 2020, and that number is projected to nearly double by 2050.
The Raw Materials: Oil and Natural Gas
Plastic production starts underground. Crude oil and natural gas contain hydrocarbons, molecules built from hydrogen and carbon atoms that serve as the chemical backbone of virtually all conventional plastics. In the United States, natural gas processing supplies the majority of the raw ingredients, while crude oil refining contributes a smaller share. Globally, the split varies by region depending on what fossil resources are locally available.
The specific hydrocarbons pulled from these sources include ethane, propane, butane, and a liquid mixture called naphtha. None of these look or feel anything like plastic on their own. They’re gases or light liquids at room temperature. Turning them into solid materials requires an intense industrial step called cracking.
How Hydrocarbons Become Plastic Building Blocks
Cracking is exactly what it sounds like: breaking larger hydrocarbon molecules into smaller, more reactive ones. In the most common method, steam cracking, ethane or propane is fed into a furnace and heated to extreme temperatures in the presence of steam. The heat snaps chemical bonds, producing smaller molecules called monomers. The two most important monomers are ethylene (two carbon atoms) and propylene (three carbon atoms). Ethylene alone is one of the highest-volume chemical products manufactured worldwide.
These monomers are small, simple molecules, but they have a useful trait: a double bond between their carbon atoms. That double bond is like a latch waiting to be opened. In the next stage, called polymerization, a catalyst breaks that double bond and allows thousands of monomer molecules to link together into long, repeating chains. These chains are polymers, and polymers are plastic in its most basic form.
Ethylene molecules chained together become polyethylene, the most common plastic on Earth, used in grocery bags, milk jugs, and plastic wrap. Propylene molecules chained together become polypropylene, found in yogurt containers, bottle caps, and car parts. Other combinations and arrangements of monomers produce the full range of plastic types: polystyrene (foam cups, packaging), PVC (pipes, flooring), PET (soda bottles, polyester clothing), and many more.
Additives That Change How Plastic Behaves
The base polymer chain is only part of what ends up in a finished plastic product. Manufacturers mix in chemical additives to give plastics specific properties like flexibility, color, durability, or fire resistance. These additives can make up a significant portion of the final material.
- Plasticizers make rigid plastic soft and bendable. Phthalates are the most widely used group, found in flexible vinyl products like flooring, wall coverings, medical tubing, and food packaging.
- Flame retardants slow or prevent burning. Polybrominated diphenyl ethers (PBDEs) are added to electronics casings, mattress foam, upholstered furniture, and textiles.
- Stabilizers and hardeners improve structure. Bisphenol A (BPA) is used to make polycarbonate plastics for food containers and baby bottles, and in epoxy resins that line the inside of metal food cans.
- Colorants, UV stabilizers, and fillers round out the list. These control appearance, prevent sun damage, and reduce manufacturing costs by bulking up the material with cheaper substances like calcium carbonate or glass fibers.
Many of these additives aren’t chemically bonded to the plastic itself. They can gradually leach out over time, which is why chemicals like phthalates and BPA show up in environmental and health research.
From Pellets to Products
Once a polymer is produced and blended with its additives, it’s typically formed into small pellets, sometimes called nurdles. These pellets are the universal currency of the plastics industry, shipped to manufacturers around the world who melt and shape them into finished goods.
The most common shaping method is injection molding. Resin pellets are loaded into a heated barrel, melted, compressed, and then forced under pressure into a metal mold carved into the shape of the final product. The plastic cools, hardens, and gets ejected. This is how most solid plastic items are made, from bottle caps to smartphone cases to dashboard components. The process is fast, precise, and scales easily to produce millions of identical parts.
Other shaping techniques include extrusion, where melted plastic is pushed through a shaped opening to create continuous forms like pipes, tubing, and plastic film. Blow molding inflates a tube of hot plastic inside a mold to create hollow objects like bottles and fuel tanks. Each method starts with the same pellets but produces very different end products.
Plant-Based and Bio-Based Alternatives
Not all plastic comes from fossil fuels. A growing category of bioplastics uses plant-derived materials as the starting point instead of petroleum. Corn starch and sugarcane are the most common feedstocks. Corn starch can be fermented into lactic acid, which is then polymerized into polylactic acid (PLA), a plastic used in compostable cups, food packaging, and 3D printing filament.
Sugarcane offers another route. Researchers have extracted cellulose from sugarcane bagasse (the fibrous material left after juice extraction) and chemically modified it into a film that can function as packaging. Other bioplastic approaches use potato starch, vegetable oils, or bacteria that naturally produce polymer chains called polyhydroxyalkanoates (PHAs).
Bioplastics still represent a small fraction of total production. They face challenges around cost, performance, and the fact that “bio-based” doesn’t automatically mean biodegradable. Some bioplastics break down in industrial composting facilities but persist in landfills or oceans just like conventional plastic. The chemistry of the final polymer, not the source of the raw material, determines whether it actually decomposes.