Forane 142b is used as a blowing agent for extruded polystyrene foam. Due to its low diffusion coefficient, Forane 142b is retained in the extruded polystyrene foam for a long time. Therefore, extruded polystyrene foam made with Forane 142b exhibits good long-term thermal insulation value, and dimensional stability. Forane 142b can also be used as part of 142b/22 (60 wt/40 wt) blend for both extruded polystyrene foam and urethane foam applications. The blend is non-flammable.