The size of lightweight JT data files containing CAD data is reduced by employing lossy compression where acceptable for portions of the CAD data, such as 3D geometry data. Dictionary-based lossless compression for the remaining portions is augmented by exploiting common repeated structures for some portions, such as precise Brep data, and compressing separate but similar data, such as all metadata for a given part and all scene graph data, together as a single block. The compressed data is then written in separate, uniquely identified data segments indexed in a table of contents, allowing quick access to any data segment for streaming.