Fill the hollow inside a 3D model
Drop the model: a closed hollow space inside shows up under the view as “Hollow inside” with its volume, and one click fills it. A broken model is repaired first, so the cavity is found even when the surface has holes.
Saves model files for your slicer, never printer code. Opened and sliced in PrusaSlicer, OrcaSlicer, Bambu Studio and Cura.
Why fill it
In a resin print a sealed pocket keeps liquid resin inside: it does not cure, and the print can crack or leak later. In an FDM slicer a cavity is a second surface, so the printer lays walls and top layers around it as well as around the outside — and what falls inside stays there. Filled, the model prints with the infill you set and nothing is trapped.
What counts as a closed hollow space
A surface inside the model that faces inwards and has no opening to the outside: a model hollowed out without drain holes, a bubble left by a CAD export, or a part placed inside a hollow one. If something sits inside the hollow, it becomes part of the solid. A model hollowed with drain holes is open to the outside — its inside is one surface with the outside and cannot be filled this way; the page says so instead of guessing.
What it does not do
It does not turn a thin shell into a solid — a model from a game or an AI generator that is only a skin with no back faces, or with walls too thin to print. That needs the shape rebuilt, not filled.
Questions
- Will the outside change?
- No. Only the inner surface is removed; every triangle of the outside stays where it was, so size and detail are the same.
- How do I know the model is hollow?
- When it opens, the facts under the view show “Hollow inside” with the number of closed spaces and their volume. The volume and weight shown are for the model as it is — after filling they go up by that amount.
- I want it hollow, but with drain holes.
- Keep the hollow and subtract a cylinder from the bottom: add a cylinder (Combine → Add a shape), move it so it reaches the cavity, and subtract it.