STL / OBJ / 3MF: How to Hand a Model to the Printer

What Each Format Does

• STL: describes surfaces with triangle meshes, accepted by nearly all slicers. Downside: geometry only, no color/material/unit, and chord-height settings can lose precision.
• OBJ: supports vertex color, material groups and multiple objects, good for colored or assembled models.
• 3MF: modern open format based on XML, carrying units, materials, metadata and even slice parameters — the first choice for new projects.

Four Checks Before Export

• Use millimeters (mm) to avoid 1000x scaling disasters.
• Outward normals, or slicing flips or errors out.
• Watertight (manifold): no holes, floating edges or duplicated faces.
• No non-manifold: each edge shared by exactly two faces.

The Slicer’s Role

CAD only defines shape; the slicer converts the mesh into paths and parameters the printer understands (layer height, supports, infill, speed). The format is just transit — slicing is the last gate that decides print quality.