Double-walled cups use air to keep coffee hot
By trapping a thin layer of air between two layers of paper, Canadian coffee shops can hold beverages at a steady temperature for over twenty minutes.
The famous Canadian 'double-cup' is more than a convenience for sensitive hands; it is a rudimentary thermal flask. When a barista nests one paper cup inside another, they create a narrow gap of trapped air that acts as a powerful insulator. This air pocket reduces heat loss through conduction by roughly 40 percent, keeping the coffee at a steady 85 degrees Celsius for nearly twenty minutes. This simple engineering trick ensures that the coffee retains its flavor profile, which relies on a precise extraction process where hot water pulls exactly one-quarter of the flavorful solids from the roasted beans.