An experimental study and a simulation model describing a coaxial tubular solar collector fabricated from polymeric materials, consisting of an inner black tube as a solar energy absorber in intimate contact with an outer transparent tube as an insulator, having the potential to provide low grade thermal energy at reasonable costs is reported. The simulation model describes the transient performance of the coaxial tubular polymeric solar collector utilizing non-linear equations solved by a difference splitting technique. The simulation model was first validated utilizing the experimental data and was then used to determine the optimal design parameters, viz. the inner, black absorber, and outer, transparent insulator, tube thicknesses. In addition, the effect of an annular air filled gap between the coaxial tubes on system, performance was also studied. The results of the experimental and simulations studies are reported together with the optimal design specifications. (C) 2003 Elsevier Science Ltd. All rights reserved.