Before You Hem a Bias Garment, Let the Fabric "Hang Out"
In "Teach Yourself to Sew: Bias basics," Threads #172 (April/May 2014) Julianne Bramson, designer and co-owner of FashionInHarmony.com, explains what bias is, how to choose the right fabric and pattern for a bias-cut design, and tips for sewing and handling these garments. Here, we share more information about how and why bias-cut fabric acts differently from on-grain fabric, and how to weight the edge of a bias-cut garment before it's hemmed.
How does the bias work?
A woven fabric's true bias is at a 45-degree angle from the straight-of-grain, or selvage edge. In the diagram above, the bias is noted by the diagonal line, which delineates the spaces between the warp and weft threads in the fabric. When fabric is used at a 45-degree angle from the straight-of-grain, the threads (warp or weft) lose their inherent stability and transform around air spaces from square to diamond shapes, as shown below. When the fabric is pulled vertically, these diamonds are long and skinny. When the fabric is pulled horizontally, the diamond shapes become short and squat.
(When fabric is rotated to the true bias, and weight is applied, the collapse of air spaces enables a fabric square to morph into a diamond shape.)