Plastics as air–liquid desiccant contacting surfaces are being explored as a promising alternative to metallic surfaces in falling film towers. Nevertheless, the poor wetness of plastics has severely restricted its extensive practical applicability. In the current experimental study, a surface modification technique is employed to enhance the dehumidification performance of single polypropylene (PP) plastic plate surface. Dehumidification ability of three kinds of plastic plate surface: plain PP plate, modified PP plate A, and modified PP plate B were investigated and compared in an adiabatic vertical falling film tower. It was found that the best modified PP plate offered 48.1–127.0% improvement in dehumidification effectiveness as compared to the plain PP plate with an average improvement of 83.3%. Furthermore, a new correlation is developed to predict the dehumidification effectiveness of plastic and metallic surfaces of adiabatic/nonadiabatic falling film tower by incorporating the wetting factor and sensible cooling information in the correlation equation. The new approach takes into account the sensible cooling (nonadiabatic absorber) of the desiccant solution in the upper half of the absorption column. The proposed correlation demonstrates excellent accord with 11 experimental datasets, with an average error of 12.7%.