Which component is NOT typically included in a drapery construction?

In drapery construction, the components primarily include face fabric, interlining, and lining on the back. The face fabric is the outermost layer that provides the decorative look of the drapery. Interlining is often used for added insulation, structure, and to enhance the fabric's appearance, while the lining on the back serves to protect the face fabric from UV rays, add weight, and improve the overall drape.

Underlayment, however, is not a typical component of drapery construction. It generally refers to a layer placed under flooring or rugs to provide cushioning or soundproofing, rather than being an element of how curtains or draperies are made. This distinction highlights the functional differences between drapery construction and other textile applications, reinforcing the understanding that an underlayment does not serve a role within the context of drapery.