Parasol is a computer program for calculating the solar and thermal properties of windows with sunshades and the energy demands of a room with a window/shading system. The program has three main features. One of them is a calculation of g, T and U for normal incidence of beam irradiation, which is performed as soon as a window or an internal/interpane sunshade is selected. The other two are based on yearly simulations, using DEROB-LTH, a building energy simulation program on which ParaSol is based. One of the applications gives the monthly average of g and T for the window glazing and the glazing/sunshade system. The other application gives the heating and cooling demands for a room with a window, with and without a sunshade, where input data are given for the internal heat, ventilation settings, shading control and temperature set-points. Version 3.0 of Parasol, which has some new and improved models, is described in this paper. The g-values obtained with this program version are compared with measurements on windows with internal/interpane screens/venetian blinds. The absolute deviation is less than 0.03 for the venetian blinds. The measured values of dark internal screens with closed air gaps exceed those simulated by Parasol, but are lower than the ones simulated with open air gaps. (C) 2006 Elsevier B.V. All rights reserved.