Conformality limitations and film composition variations inside features for films deposited at low pressures are explained using examples of studies which combine transport and reaction simulations of deposition processes and carefully designed experimental work. In the first example, the use of film profile information to decide between two kinetic models for the deposition of SiO2from TEOS is described. In the second example, composition profiles in sputter deposited Ti-W are explained in terms of titanium re-emission. Combined simulation and experimental studies of film profiles and composition profiles in features is a valuable tool in efforts to arrive at useful kinetic and transport models.