To understand the thermal fusion and interaction of porous polyurethane composites, the thermomechanical profiles of the heat-compacted composites were described and explained in line with differential scanning calorimetry analysis, FTIR-ATR interpretation, and morphological observations of the oriented ultrahigh molecular weight polyethylene (UHMWPE) under polarized light transmission. The results indicated that the as-cast polyurethane composites are porous and can be consolidated in heat compaction. The consolidated polyurethane composites displayed no thermal contraction in the thermomechanical analysis. Two polyurethane materials, Toyobo TM5 and Tecoflex 80A, were selected for the study. The differences between aromatic and aliphatic polyurethane composites were significant. Aromatic polyurethane composites exhibited characteristic thermal fusion, resulting in a uniform heat-compacted specimen that synergized the thermomechanical advantages of the polyurethane. This thermal fusion led to constraints of UHMWPE and recrystallization of both UHMWPE and polyurethane. The synergized polyurethane composite demonstrated superior resistance to thermal degradation, observed in both the individual UHMWPE and aromatic polyurethane. Thermomechanical analysis supported the recommendation of using the specific heat compaction at 115degreesC. This process rendered the aromatic polyurethane composite of highly thermomechanical stability, in agreement with previous findings related to optical transparency and tensile properties. The thermomechanical responses of the composite also provided detailed information about the differences between two samples of similar optical transparency and therefore led to the definition of the synergistic structural composite, a void-free composite with clear evidence. (C) 2004 Wiley Periodicals, Inc.