What is a Duo-tang?

A cardstock folder with a built-in three-ring binder is called a "Duo-Tang" in Canada; this is an example of a “proprietary eponym,” which is when a brand name becomes synonymous with the category. Duo-Tang, as a brand, went out of business in 2004, when Duo-Tang was purchased by Esselte.

The Duo-Tang and other folders like it used flexible metal fasteners to hold the contents contained within the cardstock covers used for presentations such as school reports. They were especially popular with students.

Esselte, a brand owned by D.C. Helms, Inc. of Phillipsburg, N.J., marketed similar products bearing the Esselte or Oxford brand name.