A truth window (or truth wall^[1]) is an opening in a wall surface, created to reveal the layers or components within the wall.^[2][3] In a strawbale house, a truth window is often used to show the walls are actually made from straw bales. A small section of a wall is left unplastered on the interior, and a frame is used to create a window which shows only straw, which makes up the inside of the wall.^[4]

Many designs exist for truth windows. Glass may be placed over the window, or an openable wooden panel, or it may be a simple framed opening.

The possible vulnerability of a truth window to moisture intrusion is sometimes raised as a concern.^[5]