Firestops have been widely applied to protect nonstructural service elements which penetrate fire resistant barriers to maintain the effectiveness of the overall fire separation. While fire stopping applications are well accepted globally, current understanding of actual fire performance is very limited and relies on standard fire test outcomes and extrapolated engineering judgement, without much scrutiny. Above all, a dearth of available thermophysical properties of common firestop materials significantly restrains the development of reliable numerical solutions. The objective of this research is therefore to optimize pseudo thermophysical properties that can be applied to model the temperature response of a typical firestop acrylic sealant. The study adopted an inverse modelling approach. Through iterative adjustment of key thermophysical parameters, a preliminary optimization for a typical firestop acrylic sealant has been attained. The simulated in-depth temperature predictions demonstrate a reasonable consistency with corresponding thermocouple data collected through customized ignition apparatus experiments. The proposed analysis methodology provides an alternative line of thought to obtain the effective thermophysical properties for fire safety designs.