Underbutton

Definition and Overview

An underbutton is a reinforcing button attached to the back side of areas such as the front placket and cuffs. It is sewn using the same thread as the outer button, spreading the pulling force applied during fastening and unfastening over a wider area. It is a trim that is not easily seen from the front and is related to garment durability and the stability of tailoring.

Materials and Structure

Underbuttons are made from materials suited to the garment application and compatibility with the outer button, such as polyester resin, shell, and nut. Since they are used on the back side, a simpler appearance than the outer button may be chosen.

The shape is generally flat with two holes or four holes. Because the outer button is supported by passing sewing thread through it, buttons with smooth hole edges and without excessive thickness are easier to handle. Shank buttons tend to create thickness or pressure, so they are not usually used as underbuttons.

How Size Is Expressed

The size of a button is shown by its diameter in mm, and may also be expressed in lignes. Lignes are a unit used for button dimensions, and in specification notation, the correspondence with mm is checked.

An underbutton must support the sewing position of the outer button while remaining inconspicuous on the back side. The size is determined by checking the size of the outer button, hole positions, textile thickness, seam allowance, and front placket specifications, then considering the required support area and the fit when worn.

Main Applications and How It Is Attached

It is used for garments that are likely to be stressed by button fastening and unfastening, such as jackets, coats, shirts, blouses, and pants. In thin textiles, low-density woven textiles, and soft textiles, it is considered to prevent tearing of the outer material and stretching at the button-attaching area.

Match the holes in the outer button and the underbutton, and attach them by passing sewing thread through both. In specifications where a thread shank is made on the outer button, adjust the thread tension so that the underbutton on the back side fits closely to the textile while maintaining proper ease between it and the outer material.

• Check whether interfacing is used and its thickness so that the load is not concentrated only on the sewn area.
• At positions that touch the skin, check for pressure caused by the edge or thickness of the underbutton.
• Before mass production, confirm ease of fastening and unfastening, and sewing strength with a prototype made using the textile.

Handling and Differences from Similar Terms

Suitability for washing or dry cleaning is affected not only by the outer button but also by the material of the underbutton. Depending on the effects of heat, detergent, solvent, and moisture, some materials may crack, chip, discolor, or change in luster. When ironing, check the product care label and the heat resistance of the trim so that direct high heat is not applied.

An underbutton is not a button used on the front side to fasten a garment, but a back-side part that reinforces the sewn area. Two-hole buttons and four-hole buttons are names based on the number of holes, while underbutton is a name based on its application. A buttonhole is the hole through which a button passes, and its role is different from that of an underbutton.

Frequently Asked Questions

Does an underbutton have to be smaller than the outer button?

It does not necessarily have to be smaller. It is selected based on fit on the back side, the hole position of the outer button, the required reinforcement area, and the thickness of the textile. However, if it is too large, it can cause pressure when worn or show through to the outer material, so it is important to check with a prototype.

Can an underbutton reinforce even thin textiles?

An underbutton helps distribute the force applied to the button-attaching area, but it is not a part that increases the strength of the textile itself. For thin or easily stretching textiles, consider using suitable interfacing and reinforcing cloth, as well as the seam specification, and confirm with a tensile test.

Can underbuttons crack or discolor after washing?

The likelihood of cracking or discoloration varies depending on the material and the washing or cleaning conditions. In particular, the effects of heat, bleach, and dry-cleaning solvents differ by material, so the suitability of both the outer button and the underbutton for the care conditions should be checked in advance.