# How to check if a mesh is watertight

Source: https://0xr.space/m/how/check-if-a-mesh-is-watertight  
Published 2026-10-10, updated 2026-10-20, by ZeroXR, the maker of Model Explorer (https://0xr.space/).

Open the file on 0xr.space, press More in the dock, then Info. The WATERTIGHT row says Yes when the surface is closed, Yes · faces flipped when it is closed but some faces point the wrong way, and No with the number of open edges and of edges shared by 3+ faces when it is not. VOLUME gives the enclosed volume in cm³ or litres. The check runs on the device, in a browser or on a Quest.

Corners are welded first, so an STL that repeats each vertex per face still reads as one surface. When the mesh is open or has flipped faces, the volume is written with a ~ as an estimate, and an open sheet that encloses nothing reads None. A rigged model, a splat or a point cloud reads Not a mesh. The check only starts when Info is opened.

## Steps

1. Open 0xr.space, press Open and choose the STL, 3MF, OBJ or GLB.
2. Press More, then Info. The bottom rows read Checking while the mesh is walked.
3. Read WATERTIGHT and VOLUME at the bottom of the panel.
4. If it is open, More, then Fix, then Clean welds split corners, drops small loose pieces and fills holes. Press Keep as new under Edit and open the copy to check it again.

## Questions

### What does shared by 3+ mean?

Edges used by three or more faces, called non-manifold. A slicer cannot tell inside from outside along them.

### Can it turn flipped faces round?

No. Fix, then Normals rebuilds the shading from the faces as they are; it does not reverse them.

### Why does my rigged character say Not a mesh?

A skinned model's rest pose is not the shape on show, so it is not checked.

### Is my file uploaded?

No. It is read and checked on the device, and nothing is sent to a server unless you create a share link yourself.

## Related guides

- [How to measure a 3D model in the browser or in VR](https://0xr.space/m/how/measure-a-3d-model-in-the-browser-or-vr)
- [How to view a 3D model at real size](https://0xr.space/m/how/view-a-3d-model-at-real-size-1-to-1)
- [How to check a 3D print's real size before printing it](https://0xr.space/m/how/check-3d-print-size-before-printing)
- [How to play a GLB animation in VR or AR](https://0xr.space/m/how/play-glb-animation-in-vr-or-ar)
- [How to hide or delete parts of a 3D model](https://0xr.space/m/how/hide-or-delete-parts-of-a-3d-model)
- [How to clean up a 3D mesh: smooth, simplify and mirror](https://0xr.space/m/how/clean-up-a-3d-mesh-smooth-simplify-mirror)