Our tester Carole tried them out for us. She started by filling one server with hot water, and another with cold.
After letting them set for a few minutes, she emptied both, and filled the hot one with soup, and the cold one with peaches.
A half hour later, the soup was still steaming and the peaches were chilled.
All-in-all, Carole gave the Insulated Stackable Servers five stars.