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The Difference Between Window Mullions and Window Muntins

Muntins and mullions are window terms that are often confused by many homeowners. It is possible that your modern windows have both muntins and mullions on them, whether in real or replicated form. In this article, Renewal by Andersen® of Long Island breaks down the differences between the two.

Difference Between Window Mullions and Window Muntins

Window Muntins

Muntin refers to the supporting bar between adjacent panes of glass. Muntin only applies to the inner vertical strips since the outer pieces that shape the frame are called stiles and riles. Muntins are frequently associated with windows, however, they can mean any kind of vertical barrier. This means they can appear on wood panels, furniture and doors as well.

Early builders utilized muntins because they were structurally critical. The outer walls of older buildings could not carry the weight when large-sized windows were installed in the walls. Muntins helped to evenly distribute the weight vertically.

Window Mullions

Like muntins, mullions also act as supporting devices. Mullions are generally described as the vertical strips that separate two sides of a single window replacement unit. Before the Victorian era, it was nearly impossible to manufacture large pieces of glass. Instead, colossal stretches of windows were achieved by holding smaller panes of glass together by these supporting bars.

Muntin vs. Mullion

Fundamentally, muntins are the vertical shafts of wood separating panes of glass in a traditional multi-pane glass composition. Mullions, on the other hand, are the single vertical props used in two-pane assemblies.

Renewal by Andersen of Long Island is a premier source of energy-efficient windows, whether traditional or specialty windows. Our team is committed to providing a cozier and more pleasant living space for you and your family through industry-leading products and expert installation skills. Call us today at (631) 843-1713 or fill out our contact form to set up an appointment. We work with homeowners in and around Huntington, NY.


"I was very impressed with Renewal by Andersen. They showed up in time and we received several follow up phone calls as the installation was being done as well as the sales representative stopping by to check in on the installation. The delivery/ installer was very professional. I would highly recommend Renewal By Andersen."

February, 18

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