File formats

A .3ds file is the format of 3D Studio for DOS, released in 1990. It stores triangle meshes, materials, cameras, lights and simple animation. For years it was the common language of 3D programs, so old model collections are still full of it. No Apple app opens it on a Mac.

3MF is an open format for 3D printing: a ZIP of XML that carries, besides a triangle mesh, units, colours, materials and the layout of the build plate. It started in 2015 from a format Microsoft donated, became the ISO/IEC 25422 standard in 2025, and PrusaSlicer, Bambu Studio and OrcaSlicer all save their projects in it. macOS can neither open nor preview it.

An .ac file is the plain-text format of AC3D, a 3D modeller Inivis has sold for Windows, Mac and Linux since 1994. It's simple and openly documented, which is why the FlightGear flight simulator, for one, uses it for aircraft and scenery. A Mac doesn't open it by itself.

AMF (Additive Manufacturing File Format) is an XML format for 3D printing that began as "STL 2.0" and has been an ASTM standard since 2011, now ISO/ASTM 52915. Compared with STL, it carries units, colours, multiple materials and even curved triangles. It never caught on widely, though, and 3MF took its place. Today you mostly come across AMF as old Slic3r and PrusaSlicer projects.

A .bgcode file is G-code that PrusaSlicer, since version 2.7, saves in binary form. Prusa says it is about 70% smaller on average. But no text editor can read it, and almost nothing outside Prusa's printers supports it. Here is what's inside, what opens it, and how to turn it back into a plain .gcode.

A .dae file is a COLLADA document: XML describing a 3D scene with meshes, materials, cameras, lights and animation. It started at Sony in 2004 and has been maintained by the Khronos Group since 2005. Game tools, SketchUp and Google Earth used it for years, but glTF is replacing it now, and Blender 5.0 removed its built-in support.

FBX is Autodesk's closed format for moving whole 3D scenes: models, materials, skeletons, animation, cameras and lights. It started in 1996 at the Canadian company Kaydara and is used mostly in film, games and AR. macOS knows the FBX type, but can neither open nor preview it by itself.

G-code is a text list of commands a printer carries out line by line: where the nozzle goes, how much material to push, which temperature to hold. A slicer writes it from a 3D model for one particular printer and adds comments with the print time, filament use and a preview. The model itself isn't in it – only the path of the nozzle.

glTF is the Khronos Group's open format for 3D models on the web, in games and in AR, with materials, textures, an object hierarchy, cameras and animation. A .gltf file is JSON that points to other files; a .glb is the same data packed into one binary file. Since 2022 glTF has been the ISO/IEC 12113 standard, and on macOS 27 even Preview opens it.

An .lwo file is a 3D object from LightWave, and an .lws file is a text scene that places such objects, adds cameras and lights, and animates them. LightWave came out in 1990 and is still sold today, but a Mac doesn't open its files by itself.

The .ms3d, .ase and .cob files are the formats of three older 3D programs: MilkShape 3D, 3D Studio MAX and trueSpace. Nobody develops two of those programs any more, and a Mac opens none of the formats by itself. You mostly find them in old game mods and model collections.

OBJ is a text format for 3D meshes that Wavefront created around 1990. Almost every 3D program and 3D-scanning app still reads and writes it. It doesn't carry colours and textures itself, though: they live in a separate .mtl file and in images, and when those get separated on the way, the model arrives white or grey.

OFF (Object File Format) is a very simple text format for polygon meshes that spread with the Geomview viewer from the University of Minnesota. It's used mostly in research: in the CGAL library, in polyhedron tools, and in machine-learning datasets such as ModelNet. A Mac doesn't open it by itself.

PLY is a simple format for 3D data that Greg Turk wrote at Stanford in 1994 for data from 3D scanners. Scanners, photogrammetry and iPhone LiDAR apps still save it today. But three different things hide behind the same extension: a coloured mesh, a point cloud and a Gaussian splat. The header tells you which one you have.

STEP (ISO 10303) is the international format CAD systems use to hand each other models with exact geometry: real cylinders, holes and fillets, not triangles. .step and .stp are the same thing. macOS can neither open nor preview it; here is what's inside and what opens it.

STL is the most widespread format for 3D printing: it describes only the surface of a model, as a list of triangles. It was created in the late 1980s at 3D Systems for stereolithography, and almost every CAD program and 3D scanner still exports it. It carries no units and no colour, and that's where most of the trouble you'll have with it comes from.

USD (Universal Scene Description) is Pixar's open format for 3D scenes, and USDZ is its packaged form, which Apple uses for AR on iPhone, iPad and Vision Pro. A scene can be stored as text (.usda), in binary (.usdc) or either way (.usd), and it can be made of many files. A Mac knows it better than almost any other 3D format: on macOS 27, Preview opens it, edits it and saves it.

X3D (Extensible 3D) is the Web3D Consortium's open ISO standard for 3D scenes and the successor to VRML from the 1990s. An .x3d file is XML describing shapes, materials, lights, viewpoints and animation. The same scene can be written in several ways, though, and not every program reads them all. macOS doesn't open X3D by itself.