What Is a Bias Cut?

A bias cut is a technique used by clothing makers to cut fabric at a diagonal angle across the weave of the fabric (called the grain) to give the material more softness and elasticity. All woven fabric is constructed by weaving warp and weft threads. The warp threads run horizontally to the bound edge of the fabric (the selvage), while the weft threads run vertically or perpendicular to the selvage. A true bias grain runs diagonally at a 45-degree angle across the weave, and fabric cut along the bias eliminates some of the tension from the weave, giving the fabric more fluidity and stretch.
https://www.masterclass.com/articles/bias-cut-guide#:~:text=...

Cutting against the normal grain of the fabric is known as a cut on the bias. When fabric is cut normally, the pattern is laid out along the grain of the weaving. The weaving lines run straight up and down, providing minimal elasticity and a very even garment.
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El corte al bies en costura
El corte al bies es una técnica empleada en costura, consiste en utilizar el tejido en sentido diagonal. Se suele usar para hacer tanto vestidos completos como en forma de tiras para ciertos acabados.
https://loheinternacional.com/es/sabes-lo-corte-al-bies/

El corte al bies o sesgo es una técnica para realizar cortes en los tejidos de forma oblicua con respecto a la dirección de los hilos. Bies es la línea que cruza la tela en diagonal de orillo a orillo formando un ángulo de 45° respecto a la trama y la urdimbre.

The bias or bias cut is a technique to make cuts in the fabrics obliquely with respect to the direction of the threads. Bias is the line that crosses the fabric diagonally from selvedge to selvedge at an angle of 45° with respect to the warp and weft.