Prediction of the flight performance of a scientific balloon is dependent on the radiative properties of the balloon. To determine its optical properties for use in performance calculations, the balloon must be viewed as a composite structure. Determination of the balloon's effective radiative properties takes into account the shape, the orientation to radiative sources, and the construction of the balloon including film properties, layers of film, and load tapes. A method for determining the effective radiative properties of a scientific balloon, that is independent of the specific constituent materials attributes, has been developed and has been applied to the standard natural shaped balloons utilized in the U. S. NASA Balloon Program. It can be applied to balloons of any size and construction for both terrestrial and planetary balloons. A commercial computer code is used to compute the total thermal radiation environment. The calculation of the effective absorptivity and effective emissivity of the balloon can now be based on the actual measured absorptivity and measured emissivity of the film and the load tapes. This new method accurately accounts for the physics and the non-uniformities of the balloon surface, and dispenses with the need for adjustments that previously required data from numerous flights. A description of the analysis approach, developed method, and results will be presented.