A mathematical model and a computer simulation program have been developed for the modelling of counterflow cooling tower splash pack thermal performance. The one-dimensional model uses basic aerodynamic, hydrodynamic and heat/mass transfer information to predict the performance of the packing material without depending on cooling tower test data. The predicted transfer characteristics and pressure drop data obtained with the simulation program are compared with experimental data. It has been found that the model predicts the correct trends for both the transfer characteristics and the pressure drop across the packing material. Quantitatively the simulation program was found to over-predict the transfer characteristics slightly and possible reasons for the differences are discussed. The predicted pressure drop data agreed closely to the experimental data. The program was used to obtain rough guidelines for optimum splash pack layout. The program was also employed to study the effect of reduced surface tension (resulting in smaller drops) on the thermal performance of splash pack.