Welcome to a type of post I like to call Fun Fact In Three Hundred Words, where I don’t waste your time yet you learn something cool in the short amount of time you spend reading my article. Without further ado, let’s begin!
I just recently learned how plastic bottles are made, of all different sizes. I don’t know if it’s how every single one is formed, but it’s at least a majority of them. Every plastic bottle begins its existence as humble plastic shards, a mix of recycled and new. 
They are then melted and poured into molds. Makes sense – but the image you see to the right of this text depicts your average one liter bottle.
How? Well, those mini things are called preforms, and are softened up by heat so they can be instantly expand into full-sized bottles, ready to be filled with all manner of tasty beverages.
Now while it is pretty cool to find out that the plastic bottles we use begin as these tiny tubes, as soon as I discovered this fact I wondered: “Why don’t they just make the molds full-sized to begin with?”
And there is, in fact, an answer to that question. It lies within the molecular structure of the bottles themselves. The plastic they are made out of is called PET, otherwise known as PolyEthylene Terephthalate. When it’s expanded from a smaller size (think: preform), the molecules “undergo strain-hardening and strain-induced crystallization, which gives the properly-made PET bottle exceptional clarity, resistance to internal pressure, uniform wall thickness, and toughness.” (source: kenplas.com) Neat, right? That’s all there is to it!
Oh, and in case your eyes glazed over while trying to read the boring text, here’s a cool three-minute clip from How It’s Made showing everything I just told you!
Cineri Gloria Sera Venit 