Schedule a Free Consultation

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.

Reviews

"Have nothing but great things to say about the window installation done today by John Hutchinson with Renewal by Andersen! He was friendly, personable and professional and did a great job installing. He did a great job of putting down roller pads and tarps with next to zero clean up. Would highly recommend them for any window replacement needed!"

Mark V.
Jun 26, 2025

"We had our new Renewal by Andersen windows installed on June 5th & 6th, 2025 and we LOVE them! The quality, beauty, and functionality are best-in-class! The whole experience from dinner presentation at Lazy River Grill, the initial in-home sales consultation and measurement, the regular communications from the salesman and concierge, and the installation team’s professionalism and skills made the process so seamless. This is the second home we have opted for Renewal windows and doors and have been delighted both times! Thank you Renewal by Andersen STL! "

Jeff C.
Jun 7, 2025

"I had an excellent experience with RbA STL. Our designer, Courtney, was great and the finished product is awesome. The installation was easy and the gentlemen left our home cleaner than they found it upon entering. I would recommend RbA STL - you’ll get tired from their constant contacts, and that’s a GOOD thing!"

Jeramy D
Jun 3, 2025

View All Reviews