A curtain (in the US, also known as a drape or drapery) is a piece of cloth intended to block or obscure light, or drafts, or water in the case of a shower curtain. Curtains hung over a doorway are known as portières. Curtains are often hung on the inside of a building's window to block the travel of light, for instance at night to aid sleeping, or to stop light from escaping outside the building (stopping people outside from being able to see inside, often for privacy reasons). In this application they are also known as "draperies." Curtains come in a variety of shapes, materials, sizes, colors and patterns, and they often have their own sections within department stores, while some shops are completely dedicated to selling curtains. An adaptation of the curtain may be a blind or, in warmer countries, such as Spain, wooden shutters that are fixed to the outside of the building to provide privacy and still keep the building cool inside. Curtains are a form of window treatment, and complete the overall appearance of the house. Window treatment helps control the ambiance and flow of natural light into the room. The effect of drapery or curtains, is best seen in daylight, and with proper indoor light positioning, it can look attractive even at night.
Curtains can be made from varying thicknesses of fabric, each with a differing degree of light absorption and heat insulating qualities. A sheer or net curtain is one that is made from translucent fabric, such as a loosely woven polyester voile or a cotton lace. Sheer curtains allow a majority of light to be transmitted through the fabric, with the fabric weave providing a basic level of UV protection while retaining maximum visibility through the curtain. Sheer curtains are sometimes referred to as privacy curtains in reference to their screening abilities; during the day most sheer fabrics will allow people inside the home to see the outside view whilst preventing people outside the home from seeing directly into the home. Due to the loose weave in sheer fabrics, these types of curtains offer very little in the way of heat insulation.
Uncoated fabrics provide the next level of heat insulation and light absorption. Uncoated fabrics consist of the vast majority of fabrics used in curtains, and are composed of a tightly woven fabric, most typically a cotton/polyester blend, which is mostly opaque when viewed in ambient light. Uncoated fabrics provide a reasonable level of heat insulation due to the tight weave of the fabric, however the fabric itself is typically not thick enough to completely absorb strong light sources. As a result, when curtains made from uncoated fabrics are closed in an attempt to block out direct sunlight, light will still be visible through the curtain.
Coated fabrics consist of a standard uncoated fabric with an opaque rubber backing applied to the rear of the fabric to provide improved light absorption. To create a coated fabric a liquefied rubber polymer is applied in a single coat to an uncoated fabric and subsequently fused dry by means of a heated roller, in much the same way that a laser printer applies toner to a sheet of paper before fusing it dry. A fabric that has been through the coating process once is considered a 1 pass coated fabric, anecdotally referred to as dim-out because of the fabric's ability to absorb approximately 50-70% of a direct light source. To improve the light absorption of a fabric it is possible to re-coat a fabric up to a maximum of 3 pass coated, which is considered sufficient to block out 100% of a direct light source, hence such fabrics are referred to as blockout coated.
Maximum light absorption and heat insulation in a curtain is created through a lined curtain, which typically consists of an uncoated fabric at the front to provide the look and feel of the curtain, with a separate coated fabric attached at the rear to provide the insulative qualities. The coated fabric is typically referred to as a lining, which simply refers to a coated fabric that does not have any particular color or pattern.
Curtains also provide visual separation in other situations, such as on a stage, where the actors make final preparations for the show behind a curtain known as the Tabs. The curtain opens when the show begins, it may close for intervals, and it closes at the end of the show.