What's a Window Mullion?

A mullion refers to the vertical piece of wood separating the panes of glass, not both the verticals and the horizontal stile pieces. Today, mullions are the vertical bars between the panes of glass in a window. As with muntins, their role is primarily decorative now.

Why do windows have mullions?

Well, mullions are vertical elements that divide two or more units of the windows. Their primary purpose is rigid support to the glazing of the window, but you can use them as a decoration, as well.

What do mullion windows look like?

Mullioned windows often have unusual shapes, and they are frequently arched at the top. Gridded windows are square or rectangular, and the grid is regular, with evenly spaced panes of glass divided into a grid, rather than large blocks of glass divided by mullions or transoms.