Glass sagging is used to process glass industrial products such as windscreens, mirrors or lenses. A 2D glass sagging process, simulated with the Finite Element Method (FEM), is presented in this work. Different thermal cases are reviewed with special care brought to radiative transfer model, with an optimized reciprocity Monte Carlo method used as the reference. Results show that ignoring radiative transfer is a too rough hypothesis. This leads to large errors on the glass temperature distribution, on the forming process and on the final shape in case of glass sagging without mold. However, predefining glass temperature or using Rosseland approximation give acceptable results, less accurate than Monte Carlo simulations especially for a fine prediction of the transfer as a function of time, but with smaller CPU times. (C) 2013 Elsevier Ltd. All rights reserved.