Abstract: A method and fastening device for attaching polyester fiber panels to a substrate, such as a wall or a ceiling. The fastening device comprises an anchor part for attachment to the substrate and a fastening part for attachment to the panel. The fastening part comprises a cylindrical portion, a helical member surrounding the cylindrical portion for penetrating the panel upon rotation of the helical member and a recess in the cylindrical portion for receiving the anchor part. The thread angle of the leading edge of the helical member is greater than the thread angle of the trailing edge.