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STEP vs IGES — which CAD exchange format should you use?

Last updated 11 June 2026

STEP and IGES are both standards-based ways to move 3D models between CAD systems. IGES came first, in 1980, and dominated for two decades. STEP arrived in 1994 and has effectively replaced it for new work. If you're choosing between the two today, the answer is STEP — but IGES still shows up in old manufacturing toolchains, and there are a handful of cases where it's actually preferred.

Head to head

Why STEP took over

Solid models, not just surfaces

IGES describes geometry mostly as surfaces and curves. To represent a solid you have to stitch surfaces together and trust the receiving system to recognise the result as enclosing a volume. That stitch step is where many IGES imports go wrong — gaps between adjacent surfaces, mismatched tangencies, tiny holes that prevent the receiver from forming a solid.

STEP describes geometry as B-rep solids directly. The face graph, the topology, the orientation of every edge — all explicit. Most STEP imports drop into the receiving CAD as a clean solid, ready to modify.

Real assemblies

STEP carries assembly hierarchy as a first-class concept: parts, sub-assemblies, transforms, names, properties. Open a STEP assembly in any modern CAD and you get the tree back. IGES has subfigure entities that can be coerced into something assembly-like, but it was always a workaround.

Manufacturing data

STEP AP242 carries Product Manufacturing Information — dimensional tolerances, surface finishes, datums, GD&T annotations. This matters for any toolchain trying to do model-based definition, where the STEP file is meant to fully replace a 2D drawing for manufacturing instructions. IGES can carry annotations but not in a way that survives a round-trip.

It's still being developed

ISO 10303 has active working groups extending STEP. AP242 keeps adding capability. IGES 5.3 was the last released revision in 1996 — the format is effectively frozen and the working group disbanded.

Where IGES still shows up

Old manufacturing toolchains

CAM software, EDM controllers, and CNC post-processors from the 1990s and early 2000s often read IGES better than STEP, or only read IGES. A shop running a 25-year-old machine may genuinely need an IGES file.

Aerospace surfaces

Some aerospace CAD workflows still use IGES for transferring surface data because the receiving tools have decades of tuned IGES import settings. STEP would work too, but the IGES workflow is already validated.

Pure surface data without volumes

If what you need to transfer is genuinely a sheet of surfaces — a styled car body panel, a sculpted aerospace skin — IGES handles surfaces natively without forcing them into a solid. Some surface modellers prefer it for that reason.

When the receiver insists

Plenty of suppliers, sub-contractors and legacy quoting systems still ask for IGES because that's what their workflow expects. Easier to send IGES than argue.

What viewers can do with each

Both STEP and IGES describe parametric / B-rep geometry. To display either, a viewer has to tessellate — convert the surfaces into triangles. Quality of viewing depends entirely on the tessellation tolerance the viewer uses, not on which format you start with.

This is why all the format guides for STEP and IGES viewing end up at the same recommendation: convert to STL or GLB for display, view the original CAD format in actual CAD software (Fusion 360, SolidWorks, FreeCAD) or a viewer with a CAD-import kernel.

The recommendation

For new work in 2026: STEP, specifically AP242. Wider support, better solids, modern.

For a legacy receiver that asks for IGES: send IGES, but also keep a STEP copy in case anything else needs it.

If you receive both: open the STEP. It will almost always import cleaner.