Expandable polystyrene (EPS) particle foams were prepared in three major steps to investigate their mechanical, thermal, and fire behavior on their degree of fusion. Bending strength was found to increase progressively, whereas compressive stress was found to increase linearly with the degree of fusion of EPS particle foams. Although at low degree of fusion the flame heights, B2 was found to decrease, it remained constant at high degree of fusion. Optical microscopic method appeared to be more reliable than pneumatic method in the determination of degree of fusion over the whole range of EPS particle foams investigated. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115:2986-2990, 2010