In a method of evaluating a product worn on a body, a computer based body sub-model of at least a portion of the body is created. A computer based product sub-model of the product is created, at least one parameter of which is variable as a function of fluid loading of the product. A computer based interaction model is also created to define instructions as to how the body sub-model and the product sub-model interact and to further define instructions corresponding to a fluid loading of the product. The body sub-model, the product sub-model and the interaction model are combined in a use model to simulate interaction between the body sub-model and the product sub-model in response to fluid loading of the product. The use model is evaluated to determine the performance of at least one product feature of the product in response to fluid loading of the product.