STEP vs IGES vs STL — Which CAD Format Should You Use?

If you regularly exchange CAD files with clients or vendors using different software, you've faced this choice: send as STEP, IGES, or STL? The three are often treated as interchangeable, but they serve very different purposes.

STEP — solid model, the safest choice for collaboration

STEP (.step/.stp) stores geometry as a solid B-rep (boundary representation) — an exact match to the original model, including precise curved surfaces. Nearly every modern CAD package (SolidWorks, Fusion 360, Inventor, FreeCAD) imports and exports STEP with high compatibility. It's the safest default when the client needs to keep editing the model in different software.

IGES — older, still used in specific industries

IGES (.iges/.igs) is STEP's predecessor, dating back to the 1980s. Some industries (especially older aerospace and automotive workflows) still require it because of legacy tooling. The downside: IGES sometimes stores surfaces as separate, unstitched patches rather than a solid — meaning small gaps between surfaces can leave the model non-watertight after re-import.

STL — a mesh, not a solid — for 3D printing and viewers

STL (.stl) is a different category entirely — not a solid model but a collection of triangle meshes approximating the surface. There's no parametric data, no editable features (holes, fillets, etc.) — just the outer shell. STL is great for 3D printing, browser-based 3D viewers, or quick visual review. Don't send STL to a client who needs to keep editing the design — they won't be able to.

• Send STEP when the client needs to keep editing the model in different CAD software.
• Send IGES only when specifically requested (legacy tooling in certain industries).
• Send STL for 3D printing, quick visual review, or embedding a web viewer.
• When in doubt, send STEP — it's the format most often requested back when the original choice turns out wrong.

All three formats can be opened and viewed directly in the browser via SyncCAD, with no CAD software install required — DWG and SLDPRT included.