Knitted Elastic

Definition and Overview

Knitted elastic is a stretch material made by knitting elastic thread with ground thread and finishing it into a tape shape. Because it is often made with raschel knitting, which is a type of warp knitting, it is also called raschel elastic. It is used for the purpose of giving garments the necessary fit while keeping them relatively soft and conforming.

The term “knitted elastic” generally refers to elastic tape made with a knitted structure. However, because the distinction between process names and product names varies by supplier or catalog, it is important to check the structure, width, and stretch characteristics in the specifications.

Materials and Structure

The thread at the core of the stretch performance is often a polyurethane-based elastic thread, with polyester, nylon, or other ground thread knitted around it. Depending on the type of ground thread, knitting density, and arrangement of the elastic thread, thickness, hand feel, stretch behavior, and recovery change.

Woven elastic has a woven structure that fixes the elastic thread with warp and weft threads, and it is generally a material with a firmer feel. Braided elastic is made by braiding threads and is also used for round or cord-like forms. Knitted elastic differs from these in that its softness and ability to conform to bending come from its knitted loops.

Checking Width and Stretch Characteristics

Width is generally shown as the dimension when the elastic is laid flat in its natural state. Because the apparent width and thickness change when it is stretched during sewing, not only the finished dimensions but also the amount of stretch during sewing are managed in the specification sheet.

Stretch may be shown as the elongation rate. This indicates how much longer it becomes when pulled relative to a reference length. However, because the results vary depending on the test load and test method, the pulling feel and recovery after stretch in the actual usage range are also checked with samples, not just the numerical value.

• Width tolerance and lot-to-lot variation
• Required stretch amount and force applied during wear
• Recovery to the original length after being stretched
• The fabric’s stretch properties and the dimensions of the sewn area

Main Applications

Knitted elastic is used for areas such as the waist, cuffs, hems, underwear, and loungewear where the garment needs to follow the body while reducing tightness. For thin garments, it is important to choose one whose thickness and firmness do not show through the surface.

It is also used for gathering. In this case, the fabric is gathered by stretching the elastic to a fixed ratio and sewing it in place. If the elastic is too weak for the application, holding power may be insufficient; if it is too strong, the wearing comfort and balance of the sewn result may be affected.

Selection and Handling Notes

When selecting it, check the width, thickness, required holding power, elongation rate, recovery, and whether it touches the skin side. When attaching it to knit or stretch materials, consider the fabric’s stretch direction and stretch amount so that only the elastic is not pulled too much.

Elastic containing polyurethane may lose stretch performance over time due to heat, ultraviolet light, sweat, sebum, detergent, bleach, and other factors. Washing, drying, and ironing conditions should be checked against the product label and material specifications, and before mass production, appearance and recovery should be confirmed through washing tests after sewing.

For storage, avoid high temperature and humidity and direct sunlight, and do not leave it in a strongly stretched state. Long-term stored items may have changed performance even if they look fine, so check stretch and recovery before use.

Frequently Asked Questions

How should knitted elastic and woven elastic be used differently?

Knitted elastic is suitable for areas where a soft hand feel and conformity to body and fabric movement are desired. Woven elastic is considered for areas where relatively firm holding power and stability are needed. However, because characteristics differ by individual specification, selection should be made by comparing them in conditions close to the intended application.

How do you determine the required length of knitted elastic?

It is not decided by simply subtracting a fixed amount from the finished circumference. Instead, it is determined by combining the fabric’s stretch, the required tightness, and the elastic’s elongation characteristics. A practical method is to change the sewing ratio in prototypes and specify it after checking the fit during wear, the amount of gathering, and the recovery after washing.

What causes knitted elastic to stay stretched after washing?

In addition to repeated pulling, the elastic thread may deteriorate due to heat, ultraviolet light, sweat, sebum, and detergent components, which can reduce recovery. Excessive stretching during sewing can also be a burden, so the handling conditions for the material and the washing conditions for the product should be confirmed in advance.