3D file formats

A 3D file can carry far more than a shape, and formats differ mainly in how much of the rest they keep:

• Geometry: vertices, faces and normals. Every format stores this.
• UVs: the 2D layout that maps textures onto the surface. See UV mapping.
• Materials and textures: anything from a single colour to a full set of PBR maps.
• Scene data: object hierarchy, pivots, transforms, cameras and lights.
• Skeletons and animation: bones, skin weights, keyframes and morph targets.

When a model "loses" something on export, it is almost always because the target format has no place to store it.

glTF is an open standard from the Khronos Group, the consortium behind OpenGL and Vulkan, designed for efficient delivery to real-time renderers. It stores geometry, UVs, PBR materials in the metallic-roughness model, scene hierarchy, skeletons, animations and morph targets. The specification fixes the conventions that cause most cross-tool problems: +Y is up, units are metres, and the coordinate system is right-handed.

It comes in two packagings with identical content. .gltf is a JSON text file that usually sits next to a .bin file of geometry and separate texture images, which suits version control. .glb is everything packed into one binary file, which suits uploading and sharing. Godot's documentation recommends glTF 2.0 as its preferred import format, and Three.js, Babylon.js, Unreal Engine and Blender all read it.

FBX is Autodesk's proprietary interchange format. It became the de facto standard for moving rigged and animated characters between modelling tools and game engines, and Unity imports it natively. Its weakness is that it is proprietary: the full specification is not public, other tools rely on the FBX SDK or on reverse-engineered readers, and materials are interpreted differently by each program. Expect to reconnect textures after import. The detail comparison is in glTF vs FBX.

OBJ, from Wavefront Technologies, is one of the oldest formats still in daily use. It is plain text, almost every 3D program reads it, and it stores geometry, UVs and normals reliably. Materials go in a companion .mtl file with a simple pre-PBR material model. It has no skeletons, no animation and, as Godot's documentation notes, no second UV channel and no PBR materials. Use it when you need a static mesh to open anywhere.

STL is the 3D-printing format. It stores a surface as raw triangles with no colour, UVs or materials, which is all a slicer needs.

USD (Universal Scene Description), from Pixar, is built for assembling very large scenes from many layered files in film and visual-effects pipelines. USDZ, a packaged variant, is the format Apple's AR Quick Look uses on iPhone and iPad.

For a static model, both formats keep the geometry and UVs intact. The differences are everything around it:

• Textures. A GLB carries its textures inside one file. An OBJ needs its .mtl file and every image to travel alongside it, with the paths intact.
• Materials. GLB stores full PBR materials. OBJ stores a basic colour and specular model, so roughness and metalness are lost.
• Size and loading. GLB is binary and loads quickly. OBJ is text, so files are larger and slower to parse.
• Scene and motion. GLB can hold several objects with their hierarchy, plus animation. OBJ holds static meshes only.

Choose GLB for the web, AR and modern engines. Keep OBJ for older software and for the rare tool that reads nothing else.

• Web, Three.js, Godot, AR on Android: GLB.
• Unity: FBX, which it imports natively. glTF also works through Unity's glTFast package.
• Unreal Engine: FBX or glTF. Both import directly.
• Blender to another DCC tool: FBX for rigs and animation, glTF for static assets with PBR materials.
• 3D printing: STL, or 3MF if your slicer supports it.
• Apple AR Quick Look: USDZ.

If a model will carry multiple LOD levels, check that your engine's import convention matches the format: Unity's automatic LOD Group setup, for example, reads _LOD0, _LOD1 meshes from a single FBX file.