Why do people use two cups instead of one to make calorimeter?

People use two cups instead of one to make a calorimeter to improve insulation and minimize heat exchange with the environment. The inner cup contains the substance being measured, while the outer cup helps to reduce heat loss or gain during the experiment. This design helps ensure that the temperature change observed is primarily due to the reaction or process occurring within the inner cup, leading to more accurate measurements. Additionally, the air gap between the two cups provides an additional layer of thermal resistance.