This is an ordinary plastic bag from a grocery store. We don’t know anything about the history of this particular bag. But you can learn a lot about plastic—and the society that makes it—by closely observing this bag through a historical lens.
The plastics industry calls this a T-shirt bag since it looks like a sleeveless, scoop-neck shirt.
The design was mass produced by Swedish plastics manufacturer Celloplast during the 1960s. Now it’s widely used in grocery stores. Other common shapes of plastic bags include zippies, gussets, doypacks, and flat polys.
Most of the bag feels slick and smooth. This bag is made from a tube of thin polyethylene film. Polyethylene is formed when molecules of ethylene gas bond together in long chains, a process called polymerization.
Side chains branching off of the main strand affect the material’s density. Low density polyethylene is a stretchy, clear plastic used in cling wrap and vegetable packaging. This bag is made of high density polyethylene (HDPE) that better resists punctures and tears.
In 1959 Swedish engineer Sten Gustaf Thulin patented an ingenious system of folds and welds that make the bag strong. The bag costs pennies to make. It can carry more than 1,000 times its own weight.
During the late 1950s dry cleaners began returning clothes to customers in polyethylene sacks. But by 1959, the clingy film bags had been linked to the accidental deaths of 80 children and 17 adult suicides. Dozens of cities proposed to ban the bags.
Manufacturers responded with a national campaign to educate consumers about the dangers of polyethylene sacks. The plastics industry adopted standards to make bags thicker and less clingy. Today five U.S. states and multiple national governments require printed warning labels.
Bill Seanor at Mobil Oil pioneered the commercial development of the T-shirt bag in the 1970s. But Mobil was committed to using low density polyethylene that stretched and tore. Seanor and his colleagues established Vanguard Plastics to make bags of HDPE.
Plastic grocery bags weren’t popular with consumers when introduced in the 1970s. Customers disliked how the bags fell over, unlike stiffer paper bags. Clerks licked their hands to open the bags, repulsing some customers. Bag makers tried to persuade customers to like them.