Muntins and Mullions: Real or Fake, They Influence Windows' Looks

Window Mullions
Window Mullions. Getty / Klaus Fenzl / EyeEm PREMIUM

Muntin and mullions are 17th century words that don't exactly roll off of your tongue. Yet it is possible that your perfectly modern house has them, whether in real or completely fake Disneyesque form.

Because the two words sound alike, they often get confused. Is a muntin the same as a mullion? And how does mutton play into this word stew? Let's unravel the mystery.

Muntin: A Divider That Carries Weight

Even though muntins today are most frequently associated with windows, they can mean any kind of vertical divider for windows, wood panels, furniture, doors, etc.

As far back as 1688, the writer R. Holme referenced "moontans and panels." Another writer, T. Smith, referenced "mountaynes" as being "six pieces of timber...ready prepared for [Westminster] chapel."  

But the clearest early definition comes in 1850, from an English architectural glossary that spoke of "English joiners [who] apply the term muntin to the intermediate upright bars of framing, and call the outside uprights styles."

Early builders used muntins because they were structurally necessary. Early buildings' outer walls could not carry the weight when large windows were placed in the walls. Muntins allowed for weight to be transmitted vertically.

Mullion: Vertical Divider For Windows

Mullions are different from muntins, though they both act as supporting devices.

The Oxford English Dictionary calls a mullion "a vertical bar dividing the lights of a window." Prior to the 19th century and the advent of inexpensive plate glass, it was impossible or prohibitive to manufacture large sheets of glass. Giant expanses of windows were achieved by holding smaller panes of glass together by supportive mullions.

So, in the truest sense, muntins are just the vertical pieces of wood separating panes of glass, not both the verticals and the horizontal stile pieces.

Is a Fake Mullion Still a Mullion?

Few window companies today make a distinction between muntins and stiles because few window buyers care about this. It's a fine distinction that rarely matters.

As a consequence, both muntins and stiles get lumped into the category of muntins. Even more frequently, both of those terms get lumped into one universal term: grille.

Major window manufacturer Pella calls all of these elements--muntin, grid, windowpane divider, or mullion--a "grille." It's a good, one-size-fits-all word for an element that no longer has structural function--it's just there for aesthetic appeal.

One of the stranger aspects of the modern house is the way that old and often unnecessary elements are retained, even after their functional use is no longer needed. The illusion of muntins is created by sandwiching thin strips of aluminum or plastic between double-paned glass, or by affixing these grilles onto the outside of the glass. They are usually offered as an add-on for an extra charge.

Why Muntin Is Not an Agricultural Product

Muntin often gets its "n" dropped, becoming "mutin" or "mutton." Both are incorrect.  

"Mutin" is not a word.  "Mutton" has nothing to do with windows or building at all; it refers to sheep meat.