Why does the tool reject my model?

The model must be a closed, consistently oriented manifold, and the cavity must remain valid after offsetting. Clean, fill holes, unify normals or repair non-manifold edges first.

Is the wall thickness exact?

The cavity is a mitered offset: flat faces target the requested value, but sharp corners and curved or concave regions can differ. Verify the actual shell with wall-thickness-check.

Does it add drain holes?

No. The result is a sealed shell with an enclosed cavity. Add a drain or vent hole in CAD or the slicer for resin printing.

Are the files uploaded?

No. Parsing, offsetting and the Manifold WASM subtraction happen in a Worker on this device; the WASM module is served as a static asset.

Why is there no drain hole in the hollow model?

The tool creates a sealed cavity and does not add drainage or vent holes. Add them in CAD or the slicer before printing, especially for resin.

Transform & optimize/Optimize

Hollow a 3D mesh (local)

Create a sealed hollow shell locally. The Worker builds a mitered inward cavity from the surface normals, subtracts it from the original with Manifold WASM, and downloads the result as binary STL without uploading the model.

ReadyNo uploadWorkerSTL · OBJ · PLY · 3MF · GLB · glTF

Tool facts

Formats: STL · OBJ · PLY · 3MF · GLB · glTF
Output: Mesh file
Worker: Yes
Max file: 500 MB
Runs: in your browser

Why local

Hollow mesh

No upload

Hollow mesh

The cavity is a mitered inward offset, then subtracted with Manifold WASM. The result is a sealed hollow shell with no drain hole; add a vent in CAD or the slicer for resin printing. Check the actual wall with wall-thickness-check before printing.

Drop a model to hollow

STL, OBJ, PLY, 3MF, GLB, or a self-contained glTF. The mesh must be closed and consistently oriented; a mitered inward cavity is subtracted and the result downloads as binary STL.

STL · OBJ · PLY · 3MF · GLB · GLTF → STL

Drop a model to hollow

STL, OBJ, PLY, 3MF, GLB, or a self-contained glTF. The mesh must be closed and consistently oriented; a mitered inward cavity is subtracted and the result downloads as binary STL.

Choose a file

Max file size: 500 MB · No upload

Wall thickness (source units)

No upload · Manifold WASM runs in the Worker.

How it works

1
Drop a closed mesh in STL, OBJ, PLY, 3MF, GLB or self-contained glTF format.
2
The Worker welds and cleans the mesh and rejects inputs that are not watertight and consistently oriented.
3
A per-vertex mitered offset is built at the requested wall thickness and checked for collapsed or flipped triangles.
4
The cavity is validated as a closed solid, subtracted from the original with Manifold WASM, and written to binary STL.
5
Download the hollow shell and verify the wall with wall-thickness-check or your slicer.

What the numbers mean

Thickness

Wall thickness is specified in the model's source units. The cavity uses mitered plane offsets, so flat faces target the requested thickness; sharp or curved regions can differ from the nominal value.

Cavity

The inner surface must be a valid closed solid before subtraction. Thin features, severe concavities or a thickness larger than the local geometry can collapse the cavity and are rejected.

Output

The result is a sealed shell with an internal cavity. It has no drain or vent hole. For resin printing, add a drain hole in CAD or the slicer; for FDM, inspect trapped air and top bridging.

Limits

This is an approximate offset shell, not a uniform-distance medial-axis offset. It does not add drain holes, self-intersection repair, or a guaranteed minimum wall. Check the result with wall-thickness-check.

Printing notes

Use a thickness that is at least two extrusion widths and verify it with wall-thickness-check.
Hollowing can create thin tips at sharp features; reduce the thickness or repair the mesh if the tool rejects the cavity.
Add a drain or vent hole before printing resin parts; the generated shell is sealed.
Keep the source file; hollowing is destructive and the result is a new STL.

Questions

References

· ISO/ASTM 52900
· Mesh offset surfaces and hollow-shell printing