How Plastic Soda Bottles Are Made Stronger Using Stretched Molecules

A 1970s invention that describes how to make lightweight, clear plastic bottles strong enough to hold carbonated drinks without exploding.

What it covers

The patent describes a process for creating a plastic bottle made of polyethylene terephthalate (PET) that is biaxially oriented. Biaxial orientation means the plastic molecules are stretched in two directions—lengthwise and widthwise—during the manufacturing process. This alignment significantly increases the strength and impact resistance of the plastic. By achieving a specific inherent viscosity and density, the resulting bottle can withstand the high internal pressure of carbonated liquids, such as soda or beer, without deforming or bursting.

What it doesn't cover

• —Does not cover bottles made from materials other than polyethylene terephthalate (PET).
• —Does not cover non-oriented plastic containers, such as simple blow-molded jugs that lack the specific molecular alignment described.
• —Does not cover the specific machinery or injection molding equipment used to stretch the plastic, only the resulting physical properties of the finished article.

The clever bit

By stretching the plastic molecules in two directions, the inventors turned a brittle polymer into a high-strength material capable of resisting the intense pressure of carbon dioxide gas.

Why it matters

This invention fundamentally changed the beverage industry by replacing heavy, breakable glass bottles with lightweight, shatterproof plastic ones. It enabled the mass distribution of carbonated soft drinks in the convenient, portable containers we use today.

Real-world examples

• 1.Standard 2-liter soda bottles
• 2.Single-serve plastic water and soda bottles
• 3.Carbonated beverage packaging