The co-solvent effect of the three solvents, ethlyene carbonate (EC), propylene carbonate (PC), and diethylene carbonate (DEC) on the composite electrolytes (CE) consisting of polyethylene oxide (PEO) and polytetramethlyene glycol-based waterborne polyurethane [WPU(PTMG)] was investigated by using a mixture design approach. The conductivity data at temperatures of 5, 25, 45 and 65 degreesC were fitted by employing a forward stepwise regression procedure. Unfortunately, as a result of negligible conductivity of EC at T-m (similar to 40 degreesC), the test statistics gave values for R-adj(2) as 0.69 and 0.71 for the regression equations at 5 and 25 degreesC, respectively. The regression equations at 45 and 65 degreesC were used to construct contour plots which facilitated the comparison of synergistic/antagonistic effects among the selected solvents. Molecular simulation was also made on the basis of the radius distribution function. The results obtained are used to interpret the results through contour plots and also using the physical properties of the solvents.