Biomimicry, the replication of natural structures, is an emerging strategy in materials engineering for developing advanced functional materials. Reptile eggshells serve as compelling models for tunable bioinspired material design due to their diversity in forms and functions. This study presents a modular approach to designing keratin-based composites with customizable vapor sorption behavior. Inspired by reptile eggshells, four key biomimetic components were reconstructed: (1) electrospun keratin membranes resembling the fibrous shell membrane, (2) an egg protein matrix replicating the proteinaceous eggshell matrix, (3) calcium carbonate (CaCO3) particles introducing mineralization, and (4) a paraffin coating representing the lipid-rich cuticle layer. The modular accuracy of these biomimetic models was validated by comparison with representative reptile eggshells through Scanning Electron Microscopy analysis and Fourier-Transform Infrared Spectroscopy. Dynamic Vapor Sorption (DVS) analysis confirmed that varying the CaCO3 content allows precise control over the absorption profiles, ranging from low to high sorption values. Additionally, integrating the organic matrix and lipid coating enabled fine-tuning of the sorption properties. The resulting biomimetic composites exhibited sorption characteristics comparable to those of natural eggshells, including Caiman crocodilus (low absorption) and Pantherophis guttatus (high absorption), demonstrating the effectiveness of the modular design strategy. These findings establish a foundation for engineering advanced biocompatible materials with adaptable sorption behavior, offering potential applications in moisture-regulating wound dressings, tissue engineering scaffolds, sustainable packaging, and filtration systems.