Barré is an unintentional repetitive horizontal pattern in fabrics that is generally undesirable and considered as a defect.
Barré occurs for many reasons associated with the manufacturing of textile ensembles like fiber, yarn, fabric manufacturing, weaving or knitting, or finishing faults.
[1][2] Barre or barrenness is a repetitious pattern in the course direction in knitted fabrics, It may involve color differences in the yarn and geometrical variations in fabric manufacturing forming the barre patterns.
[2] In knits the variation of stitch length can also cause the barre.
[4] In blends like polyester and cotton, the reason may be dyeing also.