What is Bias?
There was a time when I hated triangles. I would put a pattern together and it would end up being wonky. Then I learned about bias. Fabric has two directions of thread running through it. One goes from edge to edge (the selvages) and the other runs perpendicular to that.
CUTTING ON GRAIN
When you cut along a grain line, either the cross-grain or the length of grain, your fabric will be less likely to stretch. When cutting basic quilt blocks, make sure to cut along the grain. The long, connected single thread of the Warp or Weft makes the edge stronger. This will help ensure your quilt is square.
WHEN TO USE BIAS
You can see in this image that when you cut along the bias, there is no longer a single thread connecting the edge of the cut. This is what makes it weak and stretchy. Bias is great for making Bias Binding in garment sewing and for quilts. There is definitely a place for using bias, just not in a basic quilt block. An example of a time to be careful when cutting a quilt block to avoid bias would be when you are “fussy cutting” a particular image from a piece of fabric to show off in your quilt block.
WHAT ABOUT TRIANGLES?
With triangles, and curves for that matter, there is no way to not have a diagonal cut of some type; however, there are ways to avoid it. The trick is in how to make them. Haft Square Triangles and Flying Geese are common uses of triangles in quilts. When making 2-at-a-time or 8-at-a-time HSTs, you completely avoid the bias. When making 4-at-a-time HSTs, every edge is on the bias. At Jittery Wings, we never include the 4-at-a-time option in a pattern because it leads to frustration and wonky quilts. When making Flying Geese, we use either the 1 at a time or no-waste method.