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Muntins are strips, either functional or decorative, separating panes of glass. In the old days it was too expensive to manufacture large sheets of glass, so muntins were used to join smaller panes together and form a larger single expanse. As time went by and manufacturing techniques dropped the cost and difficulty of producing larger sheets of glass, it became functionally unnecessary to use muntins any longer in most window applications. However, the look has become associated with old fashioned or country style architecture, and now muntins are often included in windows as a decorative upgrade.

A true muntin is a strip of wood or some other material that completely separates panes of glass. But in today's windows, muntins are only illusory, sandwiches between double paned glass or affixed as a grille to their exterior. A muntin is sometimes also called a mullion, although this is a misnomer. Mullions separate window units, not individual panes of glass. Muntins are also called mutton bars, grilles, or grids.  If you have muntins in your window, you will need to keep them in mind when planning for your low E glass window replacement project or any other replacement project you may be planning.

Types of Muntins

Muntins can add a great deal of style to the exterior of a home, harkening back to yonder days and suggesting a more country style architecture. The addition of mutton bars on the windows across a front porch instantly transforms that ordinary porch into one right out of rural America. This particular design detail is so ingrained into our collective consciousness that its mere presence alone softens the design of a home and makes everything else seem more arcane and rural by extension.

Nine Light Windows

Traditional muntins divided windows into physically different sections. But today's windows only appear to do so. Often divided into nine sections, windows with muntins are commonly known as "nine light" windows. Nine lights can also be found on many front entry exterior doors. They are called nine lights because they divide the sunlight cast into the home into nine sections as it scatters across the air and onto the floor or furniture.

Full Divided Light

This gives the appearance of a window with multiple functional panes of glass. The look is achieved with exterior muntins that are permanently applied at the factory, permanent or removable interior muntins and a spacer in between the panes.

Simulated Divided Light

Windows that achieve this result have permanent muntins on their exterior and permanent or removable ones on the interior, same as full divided light models. The difference is that they do not have the spacer between the panes. This makes them cheaper while still providing a somewhat similar look as long as the inside muntin is kept in place.

Removable Interior Muntins

These are applied on the inside of the house and held in by plungers or clips. They are completely removable which makes it easier to stain or paint them. It also simplifies the task of window washing.

Finelight Muntins

Finelight muntins are grilles that are placed in between the glass panes in a dual glazed window. This look is very easy to clean and maintain, and is very modern in its appearance even as it suggests a bit of the old fashioned or classic. These can be matched to the interior color of the window but usually match the exterior frame color.

There are many different styles and varieties of window muntins on the market today. Some of them separate a window into equal sized parts like prairie muntins while others divide up the pane into unequal portions. The great variety available means buyers can choose a distinctive pattern and end up with windows that stand out from those in other homes in the neighborhood.