Individual yarns used for fabric are classified in various ways, including the amount of twist per inch or centimeter. The lowest twist yarns will have between one and five twists per inch, and are only suitable for filament yarn, which doesn’t require more twisting for strength.
In spun yarn, where twisting is needed to hold the staple fiber yarn together and strengthen it, a low twist is 5-15 twists per inch.
A low twist yarn is used in the weft of napped fabrics, where fibers from these softly twisted yarns are more easily pulled out to form the nap.