Mullions and muntins are two terms used interchangeably when referring to the vertical and horizontal lines that divide the window glass into smaller squares. However, they’re actually two different window components. Understanding what each of these terms really are allows you and your contractor to be on the same page when it comes to planning your window replacement project. Here’s a look at the differences between mullions and muntins.

All About Window Mullions
The reason why mullions and muntins are used interchangeably – aside from the fact that they sound almost the same – is that they are both vertical support components of windows. But that’s about it – mullions and muntins serve a different purpose.
Mullions are structural components separating two window units. Sometimes, they can be oriented horizontally, but their role is to separate individual windows that are installed on a large exterior wall opening. Windows, especially from centuries ago, have mullions to provide support to the assembly and keep the exterior walls secure.
All About Window Muntins
The narrow strips of wood that divide window glass into separate panes are called muntins. They’re also known as grilles, and like mullions, they served a functional purpose for windows made centuries ago. Early glassmakers couldn’t produce large pieces of glass, so they had to produce small glass panes. These are then assembled during installation, with muntins holding the individual pieces together. Today, muntins or grilles are seen as a decorative element, adding to the historical accuracy of many traditional home styles like Colonial and Tudor.
At Renewal by Andersen® of Seattle, we offer custom muntins or grilles in three different configurations: full divided light, between-the-glass and interior wood. The first one replicates the traditional muntin appearance with an exterior material made of Fibrex® and an aluminum spacer between the glass panes. You can choose the removable type or the one that’s built in between the panes. The second option is made of aluminum and is built into the window assembly so you can clean the exterior and interior glass with ease. The third option is made of hardwood and snaps into place at the interior sash.
For top-notch window installation needs, turn to Renewal by Andersen of Seattle. Schedule a free in-home consultation with us today by calling (206) 777-0954 or filling out our contact form. We serve clients in and around Bellevue.