The main purpose of the masks are to fill in the gaps of 2D textures that do not take up a whole tile. The mask textures can vary in looks depending on where the mask and the 2D texture is placed. In the hallways and Gotta Sweep's closet, the mask can be either the white brick wall or the "saloon" wooden wall texture. In the cafeteria and classrooms, the mask is always the regular white brick wall texture. In faculty rooms and the Principal's office, the mask is the same white brick wall but with green lining. In the playground and outdoor areas, the mask seems to be wooden. In the debug room, the masks are the green placeholder texture and in the library, the masks are portions of the book shelves. The masks in the mystery room is just the pitch black texture and the ceiling tile lights could either be on the regular ceiling texture, the "plastic table" ceiling texture or the blue placeholder ceiling texture.
In the original Schoolhouse, masks are unimplemented and all textures usually requiring a mask are just filled in with a regular wall texture.
- Swinging doors with the wall with molding mask, the green placeholder wall mask and the black wall mask cannot exist because swinging doors are only connected to hallways, cafeteria, library, playground, and outdoor areas.
- It is unknown how portions of book shelves could exist in real life.
- In Challenges Demo, at one point, one of the faculty rooms in the Stealthy Challenge's window masks seemed to lack a texture, causing the mask to be white. This also applied to the Grapple Challenge, but only in the first version.