The felt was somewhat a unique material that Schott use, but like the previous post said, gluing a layer of material to the rough side of leather is a standard fashion practice. It's called fusible lining/interfacing. It is to prevent stretchy leather stretch while going under the walking foot machine and getting sewn at small curved areas. It's just that Schott used a very thick fusible lining to give the stiffness, don't know why. Later on they dropped it, so if you handle the current production (actually, it's been 10 years now) HH, it's a lot softer and lighter, it's like a paper box, but supposedly will wrinkle up faster.