What makes a notebook 'premium'?

Among the products here, the premium tier is defined by paper quality (smooth, bleed- and feather-resistant stock that handles fountain-pen ink), durable binding that lays reasonably flat, and consistent build. Brands like Leuchtturm1917, Midori MD, Rhodia, and Tomoe River paper notebooks all earn high verified-purchase ratings on these traits, though the supplied data did not include independent paper-performance testing.