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The Differences Between Mullions and Muntins

The terms “mullions” and “muntins” are used interchangeably, but are actually two different window components. Knowing the difference can help make sure you and your window contractor are on the same page when designing new windows. 


Both mullions and muntins are vertical support components. Perhaps, this, along with their alliterative similarities, are the reasons why one is often confused with the other. But these are where the similarities end: these window components serve different purposes.

A mullion is a structural component that separates two window units and can sometimes be horizontally oriented. During construction, an exterior wall that’s intended to have multiple adjoining windows will have one large opening. Individual windows are separated by mullions during installation. If you intend to combine multiple windows into one large window, then your replacement window company will need to remove mullions prior to installation.


Muntins, on the other hand, are narrow strips of wood that divide window glass into separate panes and are also known as grilles. Traditionally, muntins are necessary to hold individual glass panes as early glass making technology could only produce small glass panes. Today, muntins are more of a decorative component than a structural one.

Renewal by Andersen® offers custom muntins in popular styles and are available in three configurations:

1. Full Divided Light Grilles 

These grilles replicate traditional muntins with an exterior Fibrex® material grille, an aluminum spacer between the glass panes and a removable or permanently applied interior grille.

2. Between-the-Glass 

Aluminum grilles are permanently installed between the panes, making it easy to clean the glass inside and out.

3. Interior Wood Grilles 

These decorative muntins are made of hardwood. They snap onto clips on the interior sash and can be removed for easy cleaning.

Renewal by Andersen of Wyoming is your leading provider of replacement windows and patio doors. Give us a call at (307) 472-2199. You can also fill out our contact form to schedule an appointment. We serve customers in Douglas and Casper, WY.


"We had a patio door replaced, they showed up when they said they would, they were very professional on there work and how they explained every thing they were doing. We are very pleased with the door and installation. Thanks Tony& Michelle"

Tony Geffre
Apr 11, 2019

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