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Window Mullions and Muntins – What’s the Difference

When we think about the parts that make up our windows, we usually think about panes of glass, sills, frames and casings. While you may not have heard about mullions and muntins, it is quite possible that you probably already have them on your windows or even your patio doors without even realizing it. So, what are muntins and mullions?

Window Mullions and Muntins - What’s the Difference

Window Mullions

Window mullions are the vertical bars that divide two or more panes of glass in a window. Although their main purpose is to provide rigid support, they can also serve as a decorative element. Prior to the Victorian era, it was not possible to manufacture large sheets of glass, so large expanses of windows were achieved by providing them with support via the use of mullions.

Window Muntins

Window muntins, on the other hand, are sash bars made of wood or metal strips that separate and support the glass panes in a window. Muntins only refer to the inner vertical pieces. While they are most associated with windows, they can also mean any kind of vertical divider used for doors, wood panels and even furniture.

To put it simply, muntins are inner, vertical elements that separate panes of glass in a multi-pane window while mullions are single vertical supports used in multi-pane assemblies. Not many window companies make a distinction between muntins and millions because few homeowners care about this, and, oftentimes, they are used interchangeably. A more buyer-friendly term that window manufacturers use is grille.

Whether it’s French doors or your traditional casement window, you will probably see these elements in most houses in your neighborhood. If this is something you care about when looking for windows to purchase, give Renewal by Andersen® of St. Louis a call (314) 332-2364, or fill out our contact form to speak to one of our window experts.

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Angie Klevorn
Nov 21, 2023

"3rd time using RBA for window replacement. Again, a very positive experience, the windows are great, the installation was done right, the professionalism was apparent from start to finish. Still have existing windows to be replaced and will definitely use RBA again to do it in the future."

Doug Dick
Nov 21, 2023

"Renewal by Andersen was a good experience for us in replacement of our windows. From the initial meeting with the sales representative, Leslie, through the waiting period for manufacturing, and then to the installment process, our experience was excellent! Communication is key for me and we were kept informed and updated as our windows were being ordered and manufactured. Calls to update us on the installation process were welcomed and appreciated. They know how much is too much so they don't pester you with unnecessary contact. We love our new windows!!! Did I say that already??😂 We can tell a major difference in reduced Street noise and also the temperature at our windows. Excellent company, highly recommend!!"

Paula Null
Nov 15, 2023

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