Paper curl is a persistent challenge in industrial applications, particularly in digital printing, where significant moisture is applied to paper substrates causing dimensional instability, printing defects, and material waste. We Studied on curl from two distinct mechanisms. When moisture is uniform through the sheet thickness, deformation is driven by structural asymmetry: differences in fiber orientation, density, or bonding between plies cause unequal hygroexpansion, producing structural curl. When a moisture gradient exists, an additional contribution emerges: layers with higher moisture content expand more than drier layers, superimposing moisture curl on the structural component. Isolating the structural contribution is essential: it represents the baseline curl inherent to the sheet architecture, independent of transient moisture profiles. This study focuses on structural curl in thin, freely dried paper sheets of varying density and grammage, employing a concurrent multiscale fiber network model, Brandberg et al. [1], to analyze how density variation, fiber orientation, and bonding efficiency govern moisture-induced deformation. Calibration follows has been carried on two laboratory sheet sets: low-density sheets with predominant fiber orientation, and anisotropic sheets of varying density, enabling indirect estimation of hygroexpansion properties at the fiber and bond level. Through-thickness density gradients emerge as a primary driver: higher density variation produces substantially greater curl, amplified non-linearly in heavier sheets where denser bond networks magnify differential hygroexpansion between plies. Fiber orientation anisotropy is equally critical, strongly aligned sheets exhibit pronounced directional curl, while networks approaching isotropy show more attenuated deformation. Bonding efficiency modulates curl but with much less importance. These findings establish a hierarchy of structural parameters governing paper curl, offering practical guidance for minimizing moisture-induced dimensional instability through control of density profiles, fiber anisotropy, and formation conditions.