The rewriteable dye-in-polymer optical media developed by OPTICAL DATA, INC. has been modeled using finite element analysis (FEA) to define the mechanisms which govern the write process. The purpose of performing modeling is to better understand the mechanisms for bump formation and erasure and to study the effects of varying material parameters. With the modeling results, it is intended that the material selection and the media structure can be optimized, resulting in media with improved read contrast, write sensitivity, mark edge definition, and cycling performance. The marks written on the media are created mechanically due to thermal expansion and material movement in the active film layers which are composed of dyed polymeric material. Because of this mechanical structure, finite element analysis provides a useful tool to gain an understanding of the bump formation and erasure mechanisms and the potential to predict changes which will enhance media performance. The value of finite element analysis modeling in helping to maximize performance has been described for hole forming media.1 Polymeric materials have nonlinear, time-dependent stress-strain curves compared to the linear curves for most metals and thus require different modeling considerations.2 Dye-in-polymer bump forming media offers many advantages which includes the performance characteristics of environmental stability, archivability, high storage density, and the ability to be erased and rewritten. Polymer films can also be applied by spin and web-coating techniques which, with low cost materials and high yields, offers manufacturing cost advantages. This paper will discuss thermal and mechanical deformation modeling results for air incident media during the write, or bump-forming, process. Included also are the principles of media operation, the role of media materials and the importance of understanding their properties.