# 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.

- **Patent:** US 3733309
- **Original title:** Biaxially oriented poly(ethylene terephthalate)bottle
- **Owner:** EI Du Pont de Nemours and Co
- **Granted:** 1973
- **Status:** Public domain (expired)
- **Times cited:** 170
- **Field:** consumer_electronics, materials, mechanical

## What it does

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 does NOT 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.

## Real-world examples

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

## 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.

## Frequently asked questions

### What does How Plastic Soda Bottles Are Made Stronger Using Stretched Molecules cover?

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

### Who owns patent US 3733309?

EI Du Pont de Nemours and Co owns this patent, granted in 1973.

### When does this patent expire?

This patent has expired and is now in the public domain — anyone can use the invention freely.

### What is patent US 3733309 cited by?

This patent has been cited by 170 later patents that build on its ideas.

### What problem does this patent solve?

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.

### What does this patent NOT cover?

Does not cover bottles made from materials other than polyethylene terephthalate (PET).

**Full plain-English explainer:** https://patentbrief.org/patent/us/3733309/pet-plastic-bottle

**Original patent:** https://patents.google.com/patent/US3733309

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._


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