Abstract <p>Regenerated silk fibroin (SF) and microfibrillated cellulose (MFC) offer sustainable options as the next generation of green materials based on their desirable properties for multiple applications, also, can be obtained from underutilized side streams in other industries. To date, the SF-MFC composites manufacture relies on multiple steps and cross-linking reactions, which increase their cost and footprint. We propose a sustainable and green alternative for the composite fabrication by simply inducing secondary structure formation of SF on MFC induced through methanol (MeOH) post-treatment. Molecular interactions between MFC and SF were investigated through charge density and quartz crystal microbalance experiments to determine their self-assembly mechanisms, which showed that the SF tended to adsorb on MFC without hindering its capacity to form β-sheet structures when immersed in MeOH. This methodology allowed the formation of homogeneous cryogels with low weight, good dimensional stability, and high relative porosity without the use of external agents.</p> Graphical abstract <p></p> Impact statement <p>The current high demand for bio-based materials formed through green processing is challenging for the development of versatile composites from abundant and sustainable sources. These new materials should not compete with food sources, be economically feasible, decrease carbon emissions, and provide reproducible materials properties and behaviors. This article presents a processing technique to produce silk and cellulose cryogels using only the inherent chemical properties of the bio-based polymers. The materials used were isolated from undervalued sources, such as discarded silk and sustainably harvested wood feedstocks, adding value to the producers. The self-assembled composites produced and characterized in this study exhibited properties suitable for several high-value applications due to their high porosity, thermal and dimensional stability, and water compatibility.</p>