Plastic bags start as fossil fuels, mostly natural gas, pulled from underground wells. In the United States, the primary feedstock isn’t crude oil, as many people assume. It’s hydrocarbon gas liquids, a byproduct of natural gas processing, that supply the chemical building blocks for the polyethylene resin in nearly every plastic bag you’ve carried home from a store.
The Fossil Fuel Starting Point
The journey begins at natural gas processing plants and oil refineries. When natural gas is extracted from the ground, it contains a mix of gases. Processing separates out hydrocarbon gas liquids, which include compounds like ethane and propane. These liquids are the raw ingredients for plastic production. Crude oil refineries also produce a feedstock called naphtha, which serves the same purpose, but in the U.S., natural gas byproducts dominate.
Ethane is the most important of these feedstocks for plastic bags. It’s a simple two-carbon molecule that, with the right amount of heat, can be transformed into ethylene, the single most important chemical in the plastics industry.
From Gas to Plastic Resin
The key transformation happens in a process called steam cracking. Ethane is mixed with steam and fed into a reactor heated to roughly 950°C (about 1,740°F). At that extreme temperature, the ethane molecules break apart and rearrange, producing ethylene gas as the main product along with hydrogen and methane as byproducts. Only about 38% of the material that enters the reactor emerges as usable ethylene, so the process requires enormous volumes of feedstock.
Once purified, ethylene molecules are linked together into long chains through a process called polymerization. These chains form polyethylene, the plastic resin that makes up the vast majority of grocery bags, trash bags, and retail shopping bags. The result is small, pale pellets, sometimes called nurdles, that look like tiny beads. These pellets are the universal currency of the plastic bag industry, shipped by rail and truck to manufacturers around the world.
How Pellets Become Bags
Turning resin pellets into a finished plastic bag involves a technique called blown film extrusion. The pellets are fed into a hopper that drops them into a heated extruder, essentially a long heated barrel with a rotating screw inside. The screw pushes the pellets forward while friction and external heaters melt them into a uniform molten plastic. Consistent temperature throughout the barrel is critical; uneven melting can cause the entire production run to fail.
The molten plastic is then forced through a circular die, a ring-shaped opening, and air is blown through a hole in the center of the die. This inflates the plastic into a tall, thin-walled tube, much like blowing up a balloon. The tube rises vertically, sometimes several stories high in a factory, while high-speed air rings cool it from the outside. As the tube cools and solidifies, it’s flattened between a pair of rollers, creating a double-layered flat film. That film is then wound onto rolls, cut to size, sealed at the bottom, and often printed with store logos or branding. The entire process, from pellet to finished bag, runs continuously and can produce thousands of bags per hour.
Where Most Plastic Bags Are Made
China dominates global plastic bag production by a wide margin. In 2024, China exported roughly $2.5 billion worth of plastic sacks and bags, more than four times the next largest exporter. The European Union collectively exported about $582 million, followed by India at $461 million, the United States at $368 million, and Italy at $333 million. Many countries also produce bags domestically for their own markets, so these export figures capture only part of the picture.
The global plastic bag market was valued at roughly $27.8 billion in 2025 and is projected to grow to about $39 billion by 2035. Despite bans and restrictions in many cities and countries, demand continues to rise, driven largely by retail, food packaging, and waste collection.
Bio-Based Plastic Bags
Not all plastic bags come from fossil fuels. A growing share is made from bio-based polyethylene, which starts with plants instead of natural gas. The most common feedstocks are sugarcane, sugar beet, and corn. These crops are harvested, their sugars are fermented into ethanol (the same alcohol in beer and wine), and that ethanol is then chemically dehydrated to produce ethylene, the identical molecule that comes out of a steam cracker.
From that point forward, the process is exactly the same. The bio-based ethylene is polymerized into polyethylene pellets and extruded into film. The finished product is chemically identical to a fossil-fuel bag, with the same strength, flexibility, and recyclability. The difference is upstream: the carbon in the plastic came from plants that absorbed CO₂ while growing rather than from ancient underground deposits. One trade-off worth noting is that growing the crops requires fertilizers, pesticides, and agricultural energy, which can produce their own environmental impacts that sometimes exceed those of fossil-based production.
Recycled Content Requirements
Several U.S. states now require plastic bags to contain a minimum percentage of post-consumer recycled material, meaning plastic that was used by a consumer, collected, and reprocessed into new resin. Washington state requires plastic trash bags to contain at least 15% recycled content as of 2025, rising to 20% by 2027. New Jersey follows a similar trajectory, mandating 20% recycled content by 2027. California, which has banned single-use plastic carryout bags entirely, requires paper carryout bags to contain 50% recycled content starting in 2028.
These mandates are slowly reshaping the supply chain. Manufacturers now blend virgin polyethylene pellets with recycled pellets, though the recycled material can be harder to process and sometimes produces a slightly cloudier or less uniform film. As recycled content targets climb, the infrastructure for collecting, sorting, and reprocessing used plastic bags is expanding to keep pace.