Australia's Smart Lid Systems Disposable Discoloration Cap, which automatically changes color based on the temperature of the coffee in a paper or plastic coffee cup. Smart Lid's coffee cup lid is filled with a color-changing additive that changes from brown to red when placed on a cup full of hot beverages. When the lid cools, it will return to its original brown color. There is also a device that ensures that the lid is safely placed on the cup. When the cover is discolored, a black circle forms around it, indicating that it has been correctly placed on the cup. The lid is made of unused high-strength PS (polystyrene) plastic and mixed with a color-changing additive.

Source: Guangdong Packaging