How to Read a Plastic Bag

The history of a familiar, useful, and troublesome object


Interior View of a Plastic Bag (2023)Science History Institute

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. 

Plastic Bag (2023)Science History Institute

Look at the shape

The plastics industry calls this a T-shirt bag since it looks like a sleeveless, scoop-neck shirt.

Plastic Bag (2023)Science History Institute

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.

3/4 View of a Plastic Bag (2023)Science History Institute

Feel the texture

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.

View of Weld on a Plastic Bag (2023)Science History Institute

Touch the sides and seams

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.

Warning Label on a Plastic Bag (2023)Science History Institute

Heed the warning

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.

Vanguard Logo on a Plastic Bag (2023)Science History Institute

Look for a maker’s mark

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. 

Ralphs Grocery first plastic bag (Early 1980s) by Flickr User Jericl CatScience History Institute

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.

Opening Instructions on a Plastic Bag (2023)Science History Institute

Is there a torn flap on the bag’s mouth?

One way to help clerks open bags and reduce customer gross-outs was to design a system that pulls open the next bag when the previous one is removed. Sunoco patented the “self-opening polyethylene bag stack” in 1992. Other companies patented their own methods.

Kroger Logo on a Plastic Bag (2023)Science History Institute

Who gave away this bag?

Retail companies didn’t immediately embrace plastic bags either. But they were much cheaper than paper bags. After large grocery chains Kroger and Safeway adopted plastic in 1982, the T-shirt bag soon became ubiquitous. 

Aged Plastic Bag Floating in a Wild Sea (2015-03-12) by Paolo Gamba (Flickr User Abukij)Science History Institute

Ubiquity creates problems

By 2000 the average American received 300 T-shirt bags a year. These bags don’t biodegrade. They only break into ever smaller pieces of plastic.

Recycling Symbol with Resin Code on a Plastic Bag (2023)Science History Institute

Look for a recycling symbol

Public concern about waste threatened the single use plastic market. In 1988 the Plastics Industry Association developed the Resin Identification Code to promote plastic recycling. The numbers from 1 to 7 correspond to different plastics. #2 HDPE means high density polyethylene.

Recycling Symbol with Resin Code on a Plastic Bag (2023)Science History Institute

During the 1990s plastic makers urged regulators to mandate the use of resin codes. Consumers began to separate and sort their plastic waste. This gave the impression that plastic was widely recycled. But today, less than 10% of plastic is actually recycled.

White Plastic Bag (2016-05-03) by Lasse Erkola and @laserkolaScience History Institute

Bags are particularly troublesome

Lightweight and aerodynamic, bags flutter out of bins and tangle up conveyor belts in recycling plants. In 2000, Mumbai, India, banned plastic bags. More recently, cities like Philadelphia have restricted all single-use bags, including paper bags not made with recycled material.

Messaging on a Plastic Bag to Encourage Recycling (2023)Science History Institute

Where should this bag go?

In the face of a growing number of bans, the plastic industry once again promoted consumer education and recycling. For instance, Industry supported a 2005 California law that pre-empted city taxes on single use plastic bags while requiring grocery stores to offer recycling.

Plastic Bag (2023)Science History Institute

Is this adequate?

Despite labels and store-based collection, plastic bags remain a major source of unrecycled waste. What do you see in the plastic bag’s future?

Plastic Bag (2023)Science History Institute

To learn more about the challenges and potentials of plastic, visit The Science of Stuff.

Credits: Story

Curated and written by Roger Turner
Edited by Jesse Smith
Object photography by Annabel Pinkney
Digital design by Clare Hirai

Special thanks to the following photographers:
Paolo Gamba, "Aged Plastic Bag Floating in a Wild Sea"
Lasse Erkola, "White Plastic Bag"

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.