Thermal degradation of a series of polyurethane/poly(ethyl methacrylate) interpenetrating polymer networks and their constituent networks were studied by three modes of thermogravimetric analysis : the conventional method, the constant reaction rate method, and the dynamic rate technique. The best understanding of the degradation mechanism was achieved by the last method, which allows much better resolution of overlapping events. In addition, the weight losses correspond well with the results obtained from the constant reaction rate analysis, but are achieved in shorter times.