A watertight mesh has no open boundary edges, so its surface encloses an inside and outside volume.

Boundary holes
None
Encloses
A volume
Important for
3D printing and solid operations
Not equal to
Printable

A stack of checks, not one badge

After closing boundaries, test manifoldness, self-intersections, normals, wall thickness, disconnected shells, and real-world scale.

Open-surface generation versus solid fabrication

TRELLIS.2 is designed to represent open and complex surfaces. That flexibility is different from guaranteeing a closed solid, so printing workflows need explicit repair and validation.