Which type of hair extension involves the use of heat?

Fusion extensions are the type of hair extension that involves the use of heat. This method integrates extensions by applying a keratin bond, which is melted using a heated tool. The melted keratin is then fused with the natural hair, creating a secure and long-lasting bond. This technique allows for a natural look and movement, as the extensions blend seamlessly with the client's own hair.

In contrast, clip-in extensions are temporary and do not require any heat for application; they are simply clipped into the hair. Weft extensions, while versatile, can be applied using various methods, including sew-in techniques, and typically do not involve heat. Micro-link extensions use small metal beads to attach the extensions to the natural hair and also do not employ heat for application. These differences highlight why fusion extensions are the specific method requiring heat to secure the extensions.