Canvas is the interlining that is typically found ‘floating’ between the wool outward facing panels of the jacket and the inner lining that you can see on the inside of a suit. It is typically made of loosely woven wool and horse hair, made for the specific purpose of providing structure to the front of the jacket.
Its importance lies in its role as the foundation of essentially all of the jacket’s other components, including all of the chest, lapels, pockets, and even part of the shoulders. Furthermore, it also has to conform to the shape and physique of its wearer to provide shapely drape and comfort.
Pad-stitching sewn by hand is used to facilitate this added structure and drape, and are applied meticulously and repeatedly over the entire chest, collar, and lapel of the canvas.