The performance of a kind of shape-stabilized phase change material (PCM) was demonstrated in the Testing and Demonstration Platform for Building Energy Research. The results indicate that the use of PCM could lower the indoor temperature fluctuation and slow the indoor temperature's decline rate. The PCM's performance was also simulated in BuildingEnergy, a modeling software developed by the authors and validated via experiments, and evaluated via energy saving index (ESI), an evaluation index presented by the authors. The ESI is the ratio of a particular material or component's energy saving equivalent (ESE) to the corresponding value of the ideal material or component that can maintain the room at an ideal thermal state in passive mode, where the ESE represents the hypothetical energy that should be input to maintain a passive room at the same thermal state as that when a particular material or component is adopted. The ESI can be used to characterize the performance of an actual building material or component from a common standpoint and be used to evaluate the performance of materials or components in different climatic regions or under different operating situations. The performance of the insulation material, represented by expanded polystyrene (EPS), was also simulated to give a comparison. The results show that the PCM has a better performance in the summer and a worse performance in the winter, while the EPS has a better performance over an entire year. (C) 2013 Elsevier Ltd. All rights reserved.