Cellulose nanofibril (CNF) porous structures (foams/aerogels) are typically produced using energy-intensive processes such as freeze drying. In this study, a novel microwave-assisted thawing process was developed to produce low-density (36 kg/m³) CNF foams. The process involved the freezing of CNF and urea suspension followed by immediate thawing in the microwave. A slow freezing rate produced a uniform pore structure, whereas fast freezing using liquid nitrogen resulted in the aggregation of CNF upon thawing. The in-situ carbamate crosslinking resulted from the addition of urea provided wet stability and was confirmed by FTIR and nitrogen content analysis. The compressive properties of the foams were evaluated in both dry and wet conditions. In addition, iron oxide nanoparticles were used to assess the feasibility of producing hybrid foams via this novel method. This innovative and energy-efficient approach to produce foams from cellulosic nanomaterials has the potential to be scaled up and is expected to promote the use of renewable nanomaterials in a wider range of applications.