3D file formats

A 3D file format is the container that carries meshes, and sometimes materials, animation and whole scenes, from one program to another. For game work you mostly need two kinds: the native format of your modeling tool, where you keep your working file, and an exchange format you export to the engine.

Unity's manual lists what a model file can hold: "meshes, materials, textures" and, for animated characters, animation data (Unity 6.6 Manual: Models). Not every format carries all of these.

#Format comparison

#FBX in more detail

FBX is the format you will use most for Unreal and Unity, which "still both treat FBX as the primary format in how 3D data gets into the engine" (aras-p.info: Blender FBX importer via ufbx). Aras Pranckevičius, who wrote Blender's new FBX importer, describes it as "a proprietary format that is still quite popular in some spaces" whose main downside is that "it is closed and with no public spec" (aras-p.info: Blender FBX importer via ufbx). Blender cannot use Autodesk's closed-source FBX SDK, so its developers "had to reverse engineer the format" (aras-p.info: Blender FBX importer via ufbx). He also notes that Autodesk "seems to have stopped around year 2020" developing it (aras-p.info: Blender FBX importer via ufbx).

Practical points from engine documentation:

• Export FBX rather than saving native files into the project. Unity's 2019.4 manual says "Always export Models from your 3d modeling application to FBX" (Unity 2019.4 Manual: Creating models outside of Unity).
• Do not embed textures. Unity advises against the Embed Media option, because it enlarges the project and slows import (Unity 6.6 Manual: Preparing your model files for export).
• Mind the default scale. Unity's 2019.4 manual lists a default scale factor of 0.01 for .fbx files but 1 for .blend, .ma and .mb (Unity 2019.4 Manual: Creating models outside of Unity). See units, scale and axes.
• One prop per file when using custom collision in Unreal. One checklist warns that with several meshes in one file, "only the first mesh's collision will be imported" (Cinevva: Blender to Unreal Engine Export Checklist…). See collision meshes.

Blender's FBX support is changing. Blender 4.5 added a new experimental FBX importer, written in C++ on the ufbx library and "generally 3x-15x faster than the old one"; at the time, the plan was to remove the Python importer at some point in the future (Blender Developer Documentation: Blender 4.5 LTS: Pipeline & I/O; Blender 4.5 LTS Manual: FBX). The new code only imports. Asked about a new exporter, its author replied, "if or when that will happen is anyone's guess" (Blender Developer Forum: New FBX importer: Feedback and discussion).

#Native files versus exchange files

Keep your native file as the master. Export a fresh exchange file each time it changes. Unity can import .blend, .max, .ma and .mb files directly, but it does so by launching the authoring application in the background to convert them through FBX, which needs that software installed on every machine that imports the project (Unity 6.6 Manual: Support for proprietary model file formats). Unity's own advice is to export FBX where possible (Unity 6.6 Manual: Support for proprietary model file formats).

#Common mistakes

• Relying on a format your tool is about to drop. Blender 4.5 deprecated COLLADA and announced its removal in 5.0 (Digital Production: Blender 4.5 Beta: Nodes Get Nifty, Collada…).
• Embedding textures in FBX. It bloats the project and slows import (Unity 6.6 Manual: Preparing your model files for export).
• Assuming every format carries materials and animation. Check what your target engine actually imports from each format before you commit to it.
• Re-using old export presets after a major update. Exporters and importers change between versions (Blender Developer Documentation: Blender 4.5 LTS: Pipeline & I/O).

#Further reading and watching

• units, scale and axes — the scale and axis settings that cause most export problems. Beginner. Free.