What is it?
Bias refers to the bias direction or the diagonal grain of the fabric. Just as the grain line (page link) 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 (page link) 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.
Tips for sewing on the bias
- Bias doesn’t fray! If you look closely at the edges of bias, you’ll see the woven fibers crossing each other at an angle. Try pulling on one of the threads. Unlike fabric that’s cut on the cross grain or straight grain, where you can pull a thread across the whole edge, bias fabric will not fray.
- Cut pattern pieces on the bias through a single layer, as the bias is likely to shift and stretch. You might not notice if the underneath layer has moved until after the fabric is cut.
- When sewing bias seams, slightly stretch the fabric as it goes through the machine. Alternatively, you can sew bias seams with a narrow zigzag stitch to allow the seam to stretch naturally.
- When hemming bias garments, let them hang for at least twenty-four hours. You’ll see this mentioned in pattern instructions. If you hem the garment right away, the bias sections of the hem may stretch out and hang lower than other parts of the hem and result in an uneven hemline (page link). After the twenty-four-hour period, measure the hem up from the floor and trim off evenly.
- For bias garments, the best hems are narrow hems (page link) or faced hems (page link).
- You might want to cut wider seam allowances (page link) on the bias, to allow for adjustments. This is especially helpful for delicate fabrics.
- Seam allowances on the bias don’t need to be finished, as they will not fray. You can finish them if you like. A pinked seam finish (page link) will lie flat without adding bulk. Serging bias seam allowances (page link) can create a wavy, rippled edge, so it’s not recommended.
Changing the grain line from straight to bias
You may want to change the direction of your pattern pieces to create a diagonal effect with plaid or striped fabric, or you may want a softer drape to your skirt. To change the grain line, simply draw in a new grain line that’s 45° from the original grain line. See image, right, for how.
Be careful when you’re changing the grain line. This is best to do on pieces that will not be affected by the change in drape, such as collars, cuffs, pocket pieces or waistbands. Changing major pieces of the garment from straight to bias grain will affect the fit, so proceed with caution.
Garments cut on the bias require more fabric, so if you’ve changed a garment to be cut on the bias, allow additional fabric. If you have the opportunity, take your adjusted pattern pieces to the fabric store and try them on the fabric, so you buy the right amount.
Don’t be afraid to experiment with sewing on the bias. The best way to get familiar with grain lines and working with the bias is to practice.
Drawing the bias grain line
Draw a second grain line, parallel to the first one. Connect the lines to form a square. Now create a 45° diagonal line through the corners of the box. This diagonal line is your new grain line. Easy!
Source : The Sewtionary An A to Z Guide to 101 Sewing Techniques + Definitions
About the Author : Tasia ST. Germaine