Muntin

Muntins divide a single window sash or casement into a grid system of small panes of glass, called "lights" or "lites".

Until the middle of the 19th century, it was economically advantageous to use smaller panes of glass, which were much more affordable to produce, and fabricate them into a grid to make large windows and doors.

In the UK and other countries, muntins (often called 'glazing bars' in England and 'astragals' in Scotland) were removed from the windows of thousands of older buildings during the nineteenth century in favor of large panes of plate glass.

The term 'muntin' is often confused with 'mullion' (elements that separate complete window units), and 'astragal' (which closes the gap between two leaves of a double door).

Other insulating glass arrangements include insertion of a decorative grid of simulated metal, wooden, or plastic muntins sandwiched between two large panels of glass, sometimes adding another grid of simulated wood muntins facing the interior to produce a more convincing divided light appearance.