Basically, a textile yarn is made from short fibers (like cotton, polyester, rayon, etc) spun together into a continuous yarn. A filament on the other hand is a continuous yarn produced directly by extruding synthetic filament from liquid polymer. If needed, the producer can cut the filament in short fibers. This allows the blending with other short fibers in various mixes or to permit the spinning of these short fibers in yarn form with slightly different properties than the filament. Spun yarn and filament have different properties due to the way they have been produced. The choice between the use of a spun yarn or a filament depends of the knitter or weaver's choice and the properties he is looking for in his product.