While some file-formats become unreadable after short periods, others remain interpretable over a long-term. Among the over 1.000 file-formats, some are better and some are less suited for long-term preservation. A standardized process for evaluating the stability of a file-format is described in this paper and its practical use is shown with file-formats for 3D-objects. Recommendations to users of 3D-applications are given in the last section of this article. Some of the results are used in PROBADO, a sophisticated search engine for non-traditional objects (such as 3D-documents, music etc.).