Fibre strength is highly dependent on the variety, although environmental conditions can have a small effect. Dryland cotton strength is usually not adversely affected by growing conditions. Most Australian varieties are of high strength, and local plant breeders have agreed to eliminate varieties that do not meet a minimum standard, thus keeping Australian cotton highly competitive in the world market. Fibre strength is measured by clamping a bundle of fibres between a pair of jaws and increasing the separation force until the bundle breaks.
Strength is expressed in terms of grams force per tex with the following classifications: