The main purpose of the masks are to fill in the gaps of 2D textures that don't 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, the mask can be either the white brick wall or the 'saloon' wooden wall texture. In the Cafeteria and the Classrooms, the mask is always the regular white brick wall texture. In the Faculty Rooms and the inside of the Principal's Office, the mask is the same white brick wall but with green lining. In the Playground, the mask seems to be wooden. In the Janitor's Closet, 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 or the 'plastic table' ceiling texture.
In the original Schoolhouse, the masks are unimplemented and all textures usually requiring a mask are just filled in with the regular wall texture.
- Swinging doors with the faculty mask and the green placeholder mask cannot exist because swinging doors never connect to the Principal's Office, the Janitor's Closet or the Faculty Rooms.
- In the 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 applies to the Grapple Challenge, but prior to the challenges demo V1.1.
- Upon Baldi's Basics Plus Early Access' release, the untextured mask in now transparent.
- It is unknown how portions of book shelves could exist in real life.