This paper develops a new predictive model of transient heat transfer in brine-spongy ice. It analyzes the thermal behavior and discusses the thermal response of brine-spongy ice to heat input. The model is based on the global characteristics of a mixture of ice and brine. The analytical model uses phase change characteristics of brine and ice in equilibrium states. The model involves a nonlinear partial differential equation and a number of equations of state for ice, brine, and brinespongy ice. Salinity, initial temperature, and a constant temperature for one side of the ice block, are primary variables in the studies. Samples are also tested experimentally with transient conditions and their temperature responses are captured by a thermal camera. The numerical results are closely aligned with the measured temperatures. The experiments confirm the analytical model and numerical solutions. This paper establishes new understanding of trapped brine when absorbing and releasing thermal energy through brine-spongy ice. The observations indicate a new type of ice structure with considerable differences in thermal response to transient heat transfer as compared with regular ice.