Storm Flap

Definition and Overview

A storm flap is a narrow fabric section that mainly covers the center front zipper or pocket opening. By overlapping the outside of the opening, it helps prevent rain and wind from hitting the zipper gap directly. It is used in coats, blousons, outdoor clothing, workwear, and similar items.

It is not a part of the zipper itself, but one of the sewing specifications that make up the body or pocket. In addition to the type and size of parts such as zipper teeth, sliders, top stops, and bottom stops, the width of the flap, the overlap direction, and the fastening method are designed.

Structure and Fastening

For a front opening, it is common to have a flap extend from one front panel and overlap the zipper. The width is set so it does not interfere with opening and closing and provides enough overlap when closed. In some cases, it is continued all the way to the collar or hem to cover the end of the zipper.

The flap is attached to the body with press fasteners, hook and loop, buttons, or similar closures. For pockets, a flap integrated with the pocket opening cloth may overlap the opening of the pocket bag. Depending on the application, interfacing is applied to give the shape and stabilize the edges.

• For front openings, it is a specification that covers the outside of the zipper.
• For pockets, it is used to prevent rainwater and foreign matter from entering the opening.
• A flap attached on the inside helps reduce wind penetration from behind the zipper.

Main Applications and Related Specifications

It is widely used for outerwear, rainwear, outdoor clothing, uniforms, and other items that require consideration for rain and wind. However, the storm flap alone does not determine the overall water resistance of a garment. It should be considered together with the water resistance of the outer fabric, seam finishing, and zipper specification.

A water repellent zipper reduces water ingress through the zipper itself by means of its surface and structure, while a storm flap is a specification that covers the outside or inside with fabric. A concealed front opening refers to a finish that makes the fasteners of the front opening less visible from the outside, and while it may also serve as protection against wind and rain, it is often used for design purposes as well.

Selection and Sewing Considerations

Although it is often made from the same fabric as the outer fabric, thick or stiff fabrics can make the overlapping area bulky and harder to open and close. It is important to check the fabric thickness, stiffness, presence or absence of water-repellent finishing, type of interfacing, and position of the fasteners, and to confirm zipper operability and appearance through prototyping.

In sewing, make sure the seam allowance at the flap edge does not show through to the outside, and align the stitch position and width. If the edge curls due to washing or wear, coverage performance will decrease, so adjust the grain, interfacing, and edge finishing to suit the fabric. Specify the front opening zipper length according to the finished opening, and clearly state it in the specification sheet so it is not confused with the flap foldback or the seam allowance at the collar and hem.

Frequently Asked Questions