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.
Original patent title: “Biaxially oriented poly(ethylene terephthalate)bottle”
A 1970s invention that describes how to make lightweight, clear plastic bottles strong enough to hold carbonated drinks without exploding. Granted to EI Du Pont de Nemours and Co in 1973 with 170 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
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.
The gap
What does this patent 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.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
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.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Standard 2-liter soda bottles
Single-serve plastic water and soda bottles
Carbonated beverage packaging
Why it matters
The bigger picture
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.
Filed
November 30, 1970
Granted
May 15, 1973
Market context
Who's building on this
Companies in this space
Major global packaging companies like Amcor and Berry Global continue to refine PET bottle manufacturing. The technology is now a commodity standard used by every major beverage manufacturer, including Coca-Cola and PepsiCo.
Market impact
This patent triggered a massive shift in packaging logistics, drastically reducing shipping weights and breakage costs for beverage companies. It effectively created the modern plastic bottling industry, though it also sparked long-term environmental concerns regarding plastic waste.
Claim 1 — Plain English
What this patent 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.
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.
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.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Moderate
Citation count
40/40
Highly cited
Claim breadth
0/20
Narrow claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$27K – $86K
Midpoint $54K · expired or expiring · industry ×0.9
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Claim text not yet imported for this patent
Concepts involved
Citations
Patent lineage
Cite this patent
Wyeth, N., & Roseveare, R. (1973). How Plastic Soda Bottles Are Made Stronger Using Stretched Molecules (U.S. Patent No. 3,733,309). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/3733309/pet-plastic-bottle
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
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).
Same assignee
More from EI Du Pont de Nemours and Co
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