IGES vs STEP: Which CAD Exchange Format Should You Use?

When two CAD systems need to exchange a model, the choice almost always comes down to IGES or STEP. Both are vendor-neutral, both are decades old — but they are not equals.

IGES: surfaces from 1980

IGES describes a model as a collection of surfaces and curves. There is no requirement that those surfaces form a closed, manufacturable solid — which is exactly the problem. IGES imports are notorious for gaps between faces, duplicate surfaces and "surface soup" that needs manual healing before any downstream work.

STEP: solids with structure

STEP (ISO 10303) transfers true solids: watertight B-rep bodies with topology, plus assembly structure, part names, colors and units. A STEP import is usually ready to machine, measure or modify immediately. That is why every modern workflow — and every modern CAD package — prefers it.

So why does IGES survive?

• Decades of legacy archives, especially tooling and mold data.
• Very old machines and CAM systems that predate STEP support.
• Surface-only workflows (styling, reverse engineering) where solids never existed.

Practical guidance

Sending data today? Always STEP. Received an IGES file? You can view it free in your browser or convert it to a mesh for downstream use: IGES to STL for printing, IGES to OBJ or IGES to GLB for visualization — all locally, with no upload.