Initial Graphics Exchange Specification .igs
IGES under its three-letter extension. Same 1980s standard.
What an .igs file holds
An .igs file is an IGES file; the two extensions have coexisted since three-character limits mattered. Expect surfaces rather than solids, and expect the conversion to produce shells that may not be watertight; that is a property of the format, not a failure of the conversion.
Commonly seen in: legacy CAD archives, CATIA, Siemens NX, CAM tooling.
| Data | Stored in IGS |
|---|---|
| Geometry | Yes |
| Materials and colour | Yes |
| Texture maps | No |
| Animation and rigs | No |
| Scene hierarchy | Yes |
| Read here | Yes |
| Written here | No |
Tested against a real file
The last sweep loaded Cube 10x10.igs from occt-import-js test files with its 1 sidecar files through the viewer on this site: 12 triangles across 1 meshes and 1 materials, in 2.8 seconds. Every format's result is on the test results page, run 2026-09-08.
Which way is up
IGS is a Z-up format, which most of the rest of 3D is not. Files are read exactly as written and stood up for you in the viewer; the converter has a switch for it, so a model does not arrive in the next program lying on its side.
Convert IGS to another format
Every pairing has a page saying what survives the trip.
Other things to do with an .igs file
Questions about IGS
How do I open an .igs file?
Drop it into the viewer on this site and it opens in the browser, with the scene tree, the materials and the mesh statistics. Nothing is uploaded. If you want it in another program instead, convert it to GLB, which almost everything reads.
Is IGS a good format to archive in?
IGS stores geometry, materials and colour, scene hierarchy. Anything outside that list will not be in the file at all, so archive the original alongside it if the surfacing or the rig matters.
Does converting IGS lose quality?
Geometry is copied vertex for vertex, so the shape does not degrade. What gets lost is whatever the target format has no field for: convert to STL and the materials go, convert to OBJ and the animation goes. The comparison table on each converter page says exactly which.
Formats that hold the same things
Or go back to the full format reference.