What is it? Bias

Bias refers to the bias direction or the diagonal grain of the fabric. Just as the grain line runs parallel to the selvedge, the bias runs at a 45° angle to the straight of grain. Sewing bias-cut garments is challenging, but practice will help you become familiar with the behavior of the bias and how to work with it. Fabric cut on the bias has stretch and more drape. Try pulling on your fabric along the length and then across the width. Unless it has spandex, it won’t stretch very much. Now pull on your fabric diagonally; it will have a bit of stretch along the bias. Bias is most relevant for woven fabrics. Knit fabrics  stretch across the width and sometimes the length, so working with knits on the bias is uncommon.

Cinnamon Slip (Colette Patterns) on bias

Bias pockets on a straight-grain garment, Archer Shirt (Grainline Studio)

When do you use it?

You’ll need to know where the bias is if you are instructed to cut fabric pieces on the bias. Making bias tape starts with a cut on the bias. Bias tape (page link) is great for binding curves because the natural give of the bias allows it to form around curves without puckers. Pattern pieces may be cut on the bias to give them more drape and softness. An entire garment cut on the bias will drape and cling to the body, which makes gorgeous evening dresses and lingerie. Because the bias is the diagonal direction, it means that stripes and plaids cut on the bias will turn into diagonal patterns. This can be used as a design detail for yokes, pockets, cuffs or collars. As a bonus, you won’t need to match up the lines on the bias section to the rest of the garment.