Twill Angle and Diagonal Line Direction
topic
Twill angle is determined by the ratio of warp sett to weft sett, with a 45-degree twill requiring equal warp and weft spacing in a balanced twill weave, steep twills above 45 degrees from higher warp than weft sett, and flat twills below 45 degrees from higher weft density, with S-twill ascending from lower left to upper right designated by Z direction and Z-twill ascending from lower right to upper left designated by S direction, both conventions referring to the diagonal direction matching the central portion of the corresponding letter.
Role
Governs the visual appearance of twill fabrics through the geometric relationship between thread spacing and float length that determines diagonal angle, with twill angle engineering being important for suiting and coating fabrics where the classic 45-degree twill angle of worsted suiting represents a design standard, and with twill direction being critical for face-to-face symmetry in herringbone and chevron constructions that combine S and Z twill directions.