STEP vs IGES: Which CAD File Format Should You Use?
STEP and IGES are both neutral CAD formats — they let a 3D model move between different programs without losing its solid geometry. They often appear side by side in export menus, which raises an obvious question: which one should you pick? For almost everyone today the answer is STEP. Here is why, when IGES still has a place, and how to get a clean file either way.
What “neutral format” means
Every CAD program has its own native file type, and those native files usually only open in the program that made them. A neutral format is a vendor-independent way to describe geometry so any program can read it. STEP and IGES are the two best-known neutral formats for solid and surface CAD — the common language machine shops, suppliers, and collaborators use to exchange 3D parts.
STEP (.step / .stp)
The modern standard (ISO 10303). Carries full solid geometry — a watertight, manufacturable body — reliably across programs. This is the format to hand a machine shop or supplier today.
IGES (.igs / .iges)
The older standard (from the 1980s). It mainly describes surfaces and curves rather than a single solid. Still widely accepted, but more prone to small gaps and stitching issues when re-imported.
The practical difference
The headline difference is solid vs surface. STEP transfers a part as a complete solid body, so the program that opens it knows the inside from the outside and can measure mass, generate toolpaths, and edit features cleanly. IGES often arrives as a collection of surfaces that may need to be stitched back into a solid — and if a surface is missing or has a tiny gap, that step can fail.
A simple rule
Default to STEP. It is the modern neutral format, it preserves solids, and virtually every CAD and CAM program reads it. Only reach for IGES when someone specifically asks for it — usually older software or a legacy workflow that expects surface data.
One more point worth knowing: neither STEP nor IGES is meant for 3D printing. For a printer you want a mesh format like STL or 3MF. If you are deciding between a solid format and a mesh, see STL vs STEP: which file format should you export?
When IGES still makes sense
- A shop or client asks for it by name. Some established workflows and older CAM software still expect IGES. If they request it, send it.
- Surface-only data. For complex freeform surfaces that were never a closed solid, IGES can be a reasonable carrier.
- Legacy software. Very old programs that predate broad STEP support may only import IGES.
In every other case — sending a part to a CNC shop, sharing an editable model, or archiving a design — STEP is the safer, cleaner choice. If you receive an IGES file and need to bring it in, see importing files for the formats PartWork.ai accepts.
Export a clean STEP in your browser
You do not need an expensive CAD seat to produce a proper STEP file. Describe the part you need to PartWork.ai in plain English, get editable solid geometry back, and export it directly. For machining and sharing, choose STEP; for a 3D printer, choose STL or 3MF.
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