Mesh repair tools use a lot of technical terms. This page explains what they actually mean, why they matter for 3D printing, and what Mesh2Print does to fix them.
Every 3D model is made of three building blocks:
Slicers only understand triangles, so all faces in a printable mesh must be triangulated. Most export formats (STL, 3MF) already guarantee this.
A watertight mesh is one where every edge is shared by exactly two faces — no gaps, no holes, no leaks. Imagine filling the mesh with water: none should be able to escape.
Slicers need a watertight mesh to calculate the interior correctly. If your mesh has holes, the slicer may produce incorrect infill, leave voids in the shell, or fail to slice at all.
A boundary edge is an edge that belongs to only one face. In a closed solid, every edge must be shared by exactly two faces. A lone edge means there's a hole in the mesh at that point.
Mesh2Print shows boundary edges highlighted in orange in the 3D viewer. The number of boundary edges tells you how large and complex the holes are.
A non-manifold edge is one shared by three or more faces — which is geometrically impossible in a real solid. It usually means the mesh has internal faces, duplicate geometry, or self-intersecting surfaces.
Mesh2Print highlights non-manifold edges in red. These are harder to repair automatically because the geometry is genuinely ambiguous — it's not clear which faces should be kept.
Two or more vertices at exactly the same (or nearly the same) position, but not connected. This is extremely common with STL files — the format stores each triangle independently with its own three vertices, so no vertices are ever shared.
Duplicate vertices make every edge appear as a boundary edge even when the mesh looks visually closed. Merging them fixes this instantly.
A degenerate face is a triangle with zero (or near-zero) area. This happens when two or more of its vertices are at the same position, or all three are collinear. These faces have no surface area and can confuse the slicer's calculations.
Every triangle face has a normal — a direction vector that points "outward" from the surface. The normal is determined by the order the three vertices are listed (called the winding order). Counter-clockwise = outward; clockwise = inward.
If some faces are wound the wrong way, they appear inside-out to the slicer. The slicer uses normals to determine what's inside the model and what's outside — a flipped face can create phantom voids or missing walls in the print.
Decimation reduces the number of triangles in a mesh while trying to preserve its overall shape. A high-resolution sculpt might have 2 million faces — far more than a slicer or printer needs. Reducing to 50,000 or 100,000 faces can cut file size dramatically with no visible difference in the printed result.
| Extension | Format | Notes |
|---|---|---|
| .stl | STL | Most common print format. No shared vertices — always run Merge Verts first. |
| .3mf | 3MF | Modern print format. Supports units, colors, and multi-part files. Preferred over STL. |
| .obj | Wavefront OBJ | Universal exchange format. Supported by nearly every 3D application. |
| .fbx | FBX | Common game/animation format from Autodesk. Good for complex scenes. |
| .ply | PLY | Common output from 3D scanners and photogrammetry software. |
| .glb / .gltf | glTF | Web/game standard. GLB is the binary single-file version. |
| .dae | COLLADA | XML-based interchange format used by many DCC tools. |
| .blend | Blender | Native Blender file. Requires Blender to be installed — Mesh2Print calls it headless to export geometry. |
| .mb / .ma | Autodesk Maya | Requires Maya to be installed. Mesh2Print runs mayapy to export geometry automatically. |
| .max | 3DS Max | Requires 3DS Max to be installed. Export your scene to FBX or OBJ first if you don't have 3DS Max on this machine. |
| .c4d | Cinema 4D | Requires Cinema 4D to be installed. Export your scene to FBX or OBJ first if you don't have Cinema 4D on this machine. |
The Filament Estimator gives you a rough idea of how much material your print will use and what it will cost. It uses the mesh volume calculated from your model.
How it works:
Common material densities for reference: