Wyeth's stretch-blow PET bottle held soda pressure without bursting.

Soda came in heavy, breakable glass bottles that were costly to make, ship, and collect. Plastic was light and cheap, but most plastics split under the pressure of carbonated drinks or contaminated their contents.

In 1967 DuPont engineer Nathaniel Convers Wyeth, a member of the famous Wyeth art family, started work on a lightweight plastic bottle that would not crack under the pressure of carbonation.

He settled on polyethylene terephthalate — the same material as DuPont's Mylar film — and invented a process called stretch blow molding. He molded a preform, reheated it, stretched it lengthwise, then blew it into a mold, orienting the polymer in both directions.

That biaxial orientation made the wall strong and uniform, able to withstand more than 100 pounds per square inch while staying light. The bottle received US patent 3,733,309 on May 15, 1973 and became a defining package.

Biaxially stretched plastic holds gas pressure

Stretching PET in both directions aligns chains and strengthens the wall

A thin, light bottle still holds more than 100 psi of carbonation pressure

Polyethylene terephthalate met FDA standards for food-contact purity

One molded part replaced a heavy, fragile glass container

When the incumbent is strong only because it is thick, orient the new material so it is strong while thin and light; matching the job's physics, not the old package, is the breakthrough.

The PET bottle went from zero in the mid-1970s to roughly 400 billion bottles made a year worldwide. It became both a packaging standard and a plastic-waste issue, and recycling of PET turned into a sizable stream in its own right.