If you’ve ever gone shopping for windows, you may have come across the terms “muntin” and “mullion”. The two terms often get confused, so we’re helping to clear up that confusion.

The framing that is used to separate and hold pieces of glass within a window is called a “muntin”, sometimes called “muntin bars”, “sash bars”, or “glazing bars”. Typically muntins are made of wood or metal. Historically muntins were used because it was less expensive to use smaller pieces of glass, rather than a large single pane of glass.

A mullion on the other hand is a bar or post that separates window units. Mullions are primarily a structural element, but have also been used as a decorative element in some architectural styles.