Monitoring foam expansion and the study of foaming kinetics during in-situ foam filling are essential to ensure a desirable quality of foam-filled profiles. In this current research, a novel technique is proposed for monitoring in-situ aluminum foam filling of hollow profiles. In this technique, instantaneous temperatures measured at various locations of the hollow profile being filled have been used to determine the foam expansion rate. Hence, the apparatus developed in this study is named as thermal expandometer. To demonstrate the usefulness of this thermal expandometer, aluminum foaming is performed inside a steel tube by heating the foaming precursor at different rates, and an analysis of the effect of heating rate on the foam expansion rate is presented. © 2020, The Indian Institute of Metals - IIM.