# Removing only one face of a box

Hello,

I am trying to make a box without one of its surfaces. I have realized I must use G4SubtractionSolid, but I am having no success in making a solution to remove only one face of the cube correctly. Therefore, I would be glad to learn a good solution to this problem.

Thank you!

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Boxes (`G4Box`) in Geant4 are not â€śhollow containersâ€ť. They are solid volumes. You canâ€™t just â€śremove a faceâ€ť the way youâ€™re imagining.

For a â€śbox containerâ€ť, consider a cardboard carton. In Geant4, that volume would consist of the six (or five, in your case) panels of cardboard, each with a finite, but small, thickness.

You can construct this in Geant4 in four completely different ways.

1. Use `G4Polyhedra` and make it as a single volume, by defining appropriate R-Z planes and specifying that you want four sides.

2. Use `G4SubtractionSolid` and subtract a `G4Box` corresponding to the inner empty region from a `G4Box` corresponding to the outer solid region.

3. Use `G4UnionSolid` (or better, `G4MultiUnion` to build your hollow box out of five flat `G4Box` panels, with appropriate orientation and center positions.

4. You can also place a `G4Box` of air or vacuum as a daughter volume of your solid box. But if you have anything going â€śinside the boxâ€ť, you would then have to place them as daughters of that air/vacuum volume.

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