In Part 1 (Polymer 1999;40:3685) of this series, the concept for the preparation of expandable polystyrene (PS) applying water as a blowing agent was presented. This paper focuses on the expansion characteristics of water expandable polystyrene (WEPS) beads. The influence of temperature, amount of blowing agent, molar mass of the PS matrix and slight crosslinking of the matrix were investigated in view of the expansion performance in hot air. A maximum volume expansion by a factor of 25 was achieved for WEPS in hot air (135 degrees C) as the heating medium.