What is the purpose of a mullion in construction?

A mullion primarily serves to act as a vertical or horizontal structural element that divides and supports multiple sections of a window or door. This functionality provides structural integrity by helping to bear the weight of the overall window unit, especially when dealing with large panes of glass. By distributing loads evenly, mullions prevent deformation or failure of the window assembly, ensuring stability and longevity.

While mullions can contribute to the aesthetic appeal of a window design, their main purpose centers around support and structural function. They do not inherently enhance thermal insulation but can play a role in the overall performance of a window system when integrated with other elements designed for energy efficiency.