Velvet, also known as velour, has traditionally been used as the preferred fabric for main stage curtains.

Velvet is produced from either natural or synthetic yarns and is  available in a wide range of colours and weights. In addition to providing a plush decorative cover for the proscenium opening, velvet has good acoustic and light block characteristics, thus velvet helps to block stage work lighting and deaden sounds of scene changing. Black velvet is also used for stage masking where an “ultra-black” effect is desired.

cinema curtains
cinema curtains

Brushed wool fabrics (serge etc) are normally used for stage masking as the fabric finish lights “flat”* and the weight of the fabric helps with sound deadening. Wool fabrics are available in wide range of colours and can be used as an alternative to velvet for main stage curtains; especially in applications where durability is an issue.

Satins (usually IFR synthetics) are occasionally used for main stage curtains where a noticeable sheen is desired. For a glittering effect, Organza, Lamé and other metallic weaves may also be used for main stage curtains. Due to these fabric’s lighter weight a lining maybe required. Satins and other light synthetics are also used on festoon type theatre curtains.

cinema curtains
cinema curtains

Source: http://www.theatrequip.com.au/Curtains.htm