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Difference between Single-folded Bias & Double-folded Bias

Difference between Single-folded Bias & Double-folded Bias
  • What is Bias Tape?

Many of you may know the difference between the single-folded bias and the double-folded bias, but for the new sewers there will be a brief explanation of what bias tapes are.

A bias tape refers to a long strip of fabric that is cut in a 45-degree angle to be used when finishing the raw seams. And cutting the fabric in bias’s direction means cutting at an angle of 45 degrees and not into lengthwise or crosswise grains.

The main reason for cutting in the bias direction is to give it some elasticity. This is especially important when making a curved design since it needs to be elastic to cleanly wrap the ends. Straight seams however do not necessarily require this elasticity.

Figure 1. Bias Fabric's Direction
Figure 1. Bias Fabric's Direction

At first glance, the bias tape may just look like a long cut of fabric, but the elasticity can be seen clearly by unfolding and pulling the tape.

Since the bias needs to be cut at 45 angles, instead of cutting a of a fabric that you’re using, it would be better to cut an entire portion of the fabric for the bias and then connect the cut pieces to make a bias tape roll. You can also buy and use the bias tapes that are already done for you in the stores.

Figure 2. Cutting Layout of Clothes

I normally make my bias tapes from the same fabric as the piece I am making when it is an apparel project. However, when it comes to finishing the raw seams for bags and other non visible works, I use any solid-colored bias tape in a similar shade that is available in my shelf. In particular use the bias tape that comes in rolls; bias rolls are more affordable compared to the already folded bias tapes that are sold in sewing stores.

Figure 3. Bias Cutting Image

What is the difference of Single vs Double folded Bias? 

When I first tried to buy a bias, the most confusing thing was the type of bias. The distinction between single-folded and double-folded bias and also the sizes of each bias were confusing for me. So, I'll explain how to differentiate between sizes and types for people who might be as confused as I was.

First of all, it is easier to find the answer if you think about the purpose and size of the bias you need. If I want to use a bias to finish the neck of the blouse with the following shape, I would need a single-folded bias.

Figure 4. Blouse Image

Figure 4_1. Blouse Image

Figure 4_2. Single Bias Image

When you look at the Figure 4, and 4_1 the exterior of the bias is not visible and when you take a closer look at blouse’s neckline, the same material is used as the bias. For this piece, the bias was cut out in the bias angle and was ironed in single fold. As you can tell for Figure 4_1, a different colored bias tape was used for the neckline. This was also done in single fold and in between, an elastic strip was inserted to create the elastic neck.

However, if I want a bias for the blouse below, then I need a double-folded bias instead.

Figure 5. Blouse Image

Figure 5_1. Blouse Image

Figure 5_2. Double Bias Image

The double-folded bias is probably the most commonly known bias tapes, since it is visible on the exterior of the finished piece.

To go into further detail, single- folded bias is folded inward lengthwise to the wrong side of the fabric, while the long edge would go to the center. The long ends are folded and finished, so it is used for finishing neat seams. This type of bias tape is commonly used for hemming or for simply sewing on top of fabric as decoration. For example, it is mainly used when finishing the seam allowance at the end of a skirt, the neck seam allowance of a blouse, and an armhole.

The bias treatment method using this single-folded bias is called bias facing. Bias facing is a method of treating the hem by sewing the end of the fabric with the bias end and then passing it to the wrong side, so the bias is not visible from the outside. Usually, the color of the bias is the same as the original fabric used.

Double-folded bias is a bias that folds the center of the single folded bias one more time. A single-fold bias tape has two folds, while double-fold bias tape has three. This bias is often used for migrations. Generally, the double-fold bias is used to bind the raw edge of clothes and it is visible on the inside and outside of the clothes, because of this, there are many cases where people use different color fabrics from the original fabric as decoration. And this bias tape is used in various ways such as in, quilts, aprons, wallets, and bags. If you use both tapes in the appropriate places, you can find a stylish finish for your projects.

  • How Can You Measure or Calculate Bias Size?

It is easier to understand the bias size as the size of the folded width. A bias tape marked 1/2” is 1/2” after folding the tape. If the instruction says it requires a 1/2” (13 mm) bias width, then you would need to purchase the tape that’s marked as 1/2”.  

Figure 6. 1/2" Wide Single Folded Bias

Figure 7. 1/2" Wide Double Folded Bias

The following is how to calculate and cut the bias width.

If you need to make a 1/2” wide bias, in the case of a single-folded bias, multiply 1/2” by two and cut out a 1” wide bias tape. While in the case of a double-folded bias, multiply 1/2” by four and then cut out a 2” wide bias tape.

However, if you have already cut the bias tapes yourself, the calculation never seams to be accurate. This is because you will lose some width while folding the bias tapes. If the material of the bias or the edge that needs to be finished is thicker, there needs to 1/8”-1/4” extra added to width to ease the process. But the width of the bias may vary so it is recommended cut out the bias in smaller pieces and test the widths on the raw seams, then proceed to cut the bias tape.

iThinkSew Team,

Bias Part2 -> How Much Fabric Do I Need to Make My Own Bias Tape?

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