Zipper Waviness

Definition and Overview

Zipper waviness is a condition in which, after a zipper is attached to clothing, bags, or other items, the left and right tapes, or the fabric contacting the tape, sag into a wavy shape. It not only spoils the appearance, but can also lead to resistance during opening and closing, poor engagement of the teeth, and seam distortion.

It tends to occur especially in thin fabrics, stretch materials, bias-cut sections, and long openings. However, the cause is not limited to the zipper alone; the fabric properties, interfacing, cutting, sewing conditions, and finishing processes must all be checked together.

Structure and Causes

A zipper is made up of continuous teeth, a slider that moves the teeth, left and right zipper tapes that support the teeth, and top and bottom stops or a separator. If the feed amount and stretch behavior of the tape and fabric are not uniform, excess fabric or pulling occurs on one side, appearing as waviness.

The main causes are pulling only the fabric during sewing, differences in the upper and lower materials due to presser foot pressure or feed dogs, and excessive sewing thread tension. Sewing too close to the tape edge or forcing a straight zipper onto a curved area also has an effect.

• Difference in stretch between stretch fabric and the non-stretch zipper tape
• Uneven feed amount of the fabric, tape, and interfacing
• Sewing shrinkage caused by excessive sewing thread tension
• Difference in shrinkage between the fabric and tape after washing, heat, or pressing

Specification Selection and Sewing Precautions

Teeth size affects opening and closing strength and appearance, but waviness cannot be solved by teeth size alone. While meeting the strength required for the application, choose a tape flexibility and zipper type that match the fabric thickness, stiffness, stretch, and opening shape. On thin fabrics, the tape may be more noticeable, so confirmation with a prototype is important.

Opening specifications such as open-end, closed-end, two way separator, and double slider are determined by the application. As a measure against waviness, place the fabric and zipper in their natural state before sewing, match the lengths, and temporarily secure key points. On openings that stretch easily, use stretch-resistance tape or interfacing as needed to stabilize the grain.

In general, the zipper length is checked based on the continuous tooth section from the top stop to the bottom stop, or including the separator. Distinguish between the finished opening dimension, the allowance needed to fit within the seam allowance, and the extra margin needed around the top and bottom stops, and specify the measurement points in the specification sheet.

Checks After Washing and Differences from Similar Defects

Fabric and zipper tape shrink differently after washing depending on the material and processing. Before mass production, check the waviness at the opening ends, tooth engagement, and slider opening/closing on a prototype that has been washed and pressed as intended. In some cases, it is necessary to stabilize the fabric before sewing.

Puckering is a phenomenon in which fine wrinkles caused by shrinkage gather around the seam, and it is a term that more often refers to sewing shrinkage caused by the sewing thread, fabric, and sewing conditions than zipper waviness. By contrast, waviness is used to include bending and undulation of the tape or the entire opening. Catching is a defect in which fabric or other material gets caught in the slider or teeth, and it is a separate phenomenon from waviness.

Frequently Asked Questions