Window Mullions and Muntins: A Quick Comparison

Planning a summer window installation project isn’t as simple as you might think. Because of the several factors and details involved, it can easily become stressful and time-consuming without the right window contractor. And as you go through different prospects for your replacement project, you’re also likely to hear unfamiliar terms such as “muntin” and “mullion”. If you’re not sure what these mean for your windows, here’s what you need to know: 

Window Mullions and Muntins: A Quick Comparison


A mullion is the thick vertical bar between the glass panes of a window unit. They’re not, however, referred to as the horizontal pieces but strictly the vertical wood pieces that separate the glass panes. They’re only meant to divide larger window frames while keeping them in place. They’re also referred to as the bar or post that separates two window units if they’re both attached. 


When discussing your window installation project with different contractors, mullions can sometimes refer to muntins even though they have slight differences. Muntins are referred to as the small wooden bar or any kind of vertical divider that can be on windows, doors, wood panels, and furniture. These are the vertical dividers that separate glass panes in windows. They were traditionally designed to provide additional support to the outer walls of early structures that had large windows. This structural support prevented the weight of the walls from breaking the large glass and collapsing by keeping the weight transmitted vertically.

How They Differ From Each Other

As a homeowner, you should be aware that many window companies don’t usually prioritize differentiating the two terms. This is due to how in their experience the customer tends not to take the time to know their definitions. For most contractors, it’s easier to consider both of them as window grilles as this is a more generalized term that also refers to other relative terms such as window grids and pane dividers.

Today’s muntins and mullions are usually made the same way by sandwiching thin strips of aluminum or plastic between a double-paned glass. This makes them less of a functional window component and more of ornamental decoration. While they don’t affect the window’s performance, it still helps to understand their key differences especially if you’re planning to add them as part of your exterior design. 

If you’re looking for reputable window installation services, Renewal by Andersen® of San Francisco has got you covered! Call us today at (866) 609-5033, or fill out our convenient online form. We serve customers in San Francisco, CA, and nearby communities.

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