Elastic Performance in Garment Making
When you’re designing garments with stretch fabrics—like swimwear or dancewear—the type of elastic you choose can have a big impact on the fit and functionality of the garment. Elastic is essential in areas where you need a snug fit, like waistbands, leg openings, and armholes. But how do you ensure the elastic is the right size and tension? Let's explore how to calculate elastic tension and properly reduce the elastic to fit your garment.
Choosing the Right Elastic
Before jumping into how to reduce elastic, it’s important to understand that not all elastics are created equal. Elastic can come in different widths, thicknesses, and materials, and each one has different stretch and rebound properties. Typically, you'll encounter three types of elastics:
- Woven Elastic: This type of elastic doesn’t roll easily and is strong, but it doesn’t stretch as much. It’s great for waistbands in heavier garments but might not be ideal for garments that need a lot of flexibility.
- Knitted Elastic: This is soft and flexible, commonly used in lighter garments like lingerie. However, it may not offer enough tension for areas needing more support, like waistbands in activewear.
- Rubber Elastic: This is strong, thin, and used often in swimwear. It provides more rebound tension, making it suitable for garments that need to stay snug, even when wet.
The type of elastic you choose should match the needs of your garment and the fabric’s stretchiness.
How Tight Should Elastic Be?
Elastic tension is key to ensuring a garment fits snugly without being uncomfortable. To understand this, you’ll need to calculate the amount of negative ease—how much smaller the garment is compared to the body—and the amount of tension the elastic should apply.
But first, let’s talk about stretchability. Different fabrics and elastics stretch differently. In the steps that follow, we’ll calculate the stretch of both the fabric and the elastic and show you how to reduce the elastic so that it fits perfectly within your garment.
---How to Reduce Elastic for Garments
To sew elastic into a garment, the elastic needs to be slightly shorter than the fabric to create tension, ensuring the garment fits snugly. This shortening of the elastic is called elastic reduction. The goal is to figure out how much shorter the elastic should be compared to the fabric based on the fabric’s stretchiness.
Step 1: Test the Fabric Stretch Ratio
Before calculating how much to reduce the elastic, you need to understand how much the fabric itself stretches. Here's how:
- Cut a small strip of fabric—about 10 cm is a good length.
- Stretch the fabric by hand to see how far it comfortably stretches. Let’s say your 10 cm strip stretches to 12 cm.
- Calculate the Fabric Stretch Ratio:
(Stretched Fabric Length - Original Fabric Length) Original Fabric Length × 100
Using our example:
(12 cm - 10 cm) 10 cm × 100 = 20%
This means the fabric can comfortably stretch 20% beyond its original length.
Step 2: Test the Elastic’s Stretch
Next, you need to test how much the elastic stretches:
- Cut a piece of elastic—about 10 cm.
- Stretch the elastic by hand to see how far it comfortably stretches before feeling too tight. If your 10 cm elastic stretches to 11.5 cm, this is how much it stretches comfortably.
- Calculate the Elastic Stretch Percentage:
(Stretched Elastic Length - Original Elastic Length) Original Elastic Length × 100
Using the example:
(11.5 cm - 10 cm) 10 cm × 100 = 15%
This means the elastic can stretch 15% beyond its original length comfortably.
Step 3: Determine the Total Stretch for Your Garment
Now that you know how much the fabric and elastic can stretch, you need to decide how much total stretch you want in the garment. This is the combined stretch from the fabric and elastic.
Let’s say you want 15% total stretch when the garment is worn.
- The fabric already stretches 10% based on its stretch ratio.
- To reach 15% total stretch, the elastic needs to provide an additional 5% tension.
Here’s the formula:
Elastic Tension = Total Stretch - Fabric Stretch Ratio
For this example:
Elastic Tension = 15% - 10% = 5%
Step 4: Calculate the Elastic Length
Now that you know the elastic needs to provide 5% tension, you can calculate how much to reduce the elastic:
If the waistband measures 63 cm when unstretched, and you want the elastic to stretch by 5%, here’s how to calculate the new elastic length:
Fabric Length (1 + Elastic Tension Percentage)
For this example:
63 cm 1.05 = 60 cm
This means you need to cut the elastic to 60 cm, so it will stretch 5% when sewn into the garment.
How to Sew Elastic Into Garments
Once you’ve calculated the right length for your elastic, it’s time to sew it into your garment. Here are a few common methods for sewing elastic:
1. Sew Elastic Using a Fold-Over Method
This is one of the most popular methods for attaching elastic. You sew the elastic directly onto the wrong side of the fabric, fold it over, and topstitch it down:
- Position the elastic: Align the elastic on the wrong side of the fabric at the edge where it will be sewn.
- Sew the elastic: Use a zigzag stitch or serger to sew the elastic onto the fabric, stretching the elastic slightly as you sew.
- Fold the elastic over: Fold the elastic and fabric edge over, enclosing the elastic. Topstitch using a zigzag stitch or coverstitch.
2. Sew Elastic Into a Casing
If you prefer not to sew directly onto the elastic, you can create a fabric casing and insert the elastic inside:
- Sew the casing: Fold the edge of the fabric to create a tunnel (or casing) wide enough to fit the elastic, and stitch it down, leaving a small opening.
- Insert the elastic: Thread the elastic through the casing using a safety pin or bodkin.
- Sew the ends of the elastic together: Once the elastic is fully inside the casing, overlap the ends by about 1 cm and stitch them together.
- Close the opening: Sew the opening of the casing closed to finish.
3. Sew Elastic Into Bound Seams
For straps or edges that need to stay strong but flexible, you can use bound elastic:
- Cut a narrow strip of fabric: Cut a narrow strip of fabric to bind around the elastic.
- Position the elastic: Place the elastic inside the fabric strip and fold the fabric around it.
- Stitch the binding: Use a zigzag or straight stitch to sew the fabric around the elastic, creating a neat, bound edge.
4. Sew Elastic with Concealed Seams
For a cleaner look, you can sew elastic with concealed seams. This method hides the elastic inside two layers of fabric:
- Sandwich the elastic: Place the elastic between two layers of fabric, aligning the edges.
- Sew the layers together: Use a zigzag or stretch stitch to sew through both fabric layers and the elastic, ensuring it’s enclosed and hidden within the seam.
- Finish the seam: Once the elastic is securely sewn, you can topstitch the seam for added durability or leave it clean for a seamless look.
Final Thoughts on Sewing Elastic
The method you choose for sewing elastic depends on the garment, the fabric, and the look you want to achieve. Whether you're sewing a waistband, leg opening, or armhole, ensuring the elastic is correctly reduced and attached will give you a great fit that lasts.