Millions of small links, joined into chains
What Is Plastic Actually Made Of?
Plastic is enormous molecules built by joining one small unit to itself over and over into long chains.
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Step 1 of 5
A plastic molecule is one shape, repeated.
Take a small molecule, join it to an identical one, and keep going. After a few thousand you have a single molecule long enough to tangle.
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Step 2 of 5
The links mostly come from oil and gas.
Crude oil is a soup of carbon chains. Refining sorts them, and cracking snaps the big ones into the small reactive units the chains are built from.
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Step 3 of 5
How the chains sit decides what it feels like.
Loosely tangled chains give a soft squeezy bottle. Chains lying neatly alongside each other give a stiff, strong, harder plastic.
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Step 4 of 5
Most plastics melt, which is why they can be moulded.
Heating loosens the tangle so the chains slide, without breaking the chains themselves. Cool it in a mould and the tangle sets in that shape.
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Step 5 of 5
There is no such thing as just plastic.
The recycling number on the bottom says which chain it is. They melt at different temperatures and will not mix, which is why sorting matters so much.
A single polythene chain in a carrier bag can be over 100,000 atoms long. Straightened out, the chains from one bag would stretch further than you could walk in a day.
The short version
Plastic is one small molecule joined to itself thousands of times, and how those long chains lie decides whether it is floppy or stiff.
Try it yourself
Look at the little triangle on the base of three different containers. Different numbers mean genuinely different molecules, not just different colours.
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