An effective backrest in weaving ensures an efficient sensing and tension regulating mechanism, and backrest position has a direct effect on low stress mechanical properties. An overview of backrest performance in recently developed letoff mechanisms reveals that the ideal positive letoff features the maintenance of a constant length between the backrest and the fell of the fabric; a constant warp tension throughout weaving; and adjustments of the warp delivery rate that allow for slight variations in warp tension. The types of backrests include conventional flat or stationary backrests; oscillating backrests for semiautomatic looms, and sensitive backrests for fully automatic and shuttleless looms. An analysis of backrest dynamics for freely rotating back rollers and friction at the back roller clarifies the relationship between warp tension and beam diameter during weaving.