The 1985 McDLT advertising campaign promoted the McDLT sandwich.
The McDLT was designed around separate packaging: the hot side held the meat and the cool side held the lettuce, tomato, and other cold ingredients. Customers were expected to combine the two sides before eating. The concept made temperature separation the central selling point rather than simply adding another variation to McDonald’s burger menu.
The campaign became famous for its unusual two-compartment container and the phrase “Keep the hot side hot and the cool side cool.” Jason Alexander appeared in a well-known commercial for the product before becoming widely known for his later television role.
The McDLT is sometimes confused with the Big Mac because both were prominent McDonald’s hamburgers, but they had different constructions and advertising identities. The product was eventually discontinued, making the campaign a notable example of a short-lived McDonald’s branding experiment.