Abstract This research explored the thermal conductivity (k value) and thermal resistivity (R-value) of bio-waste cellulosic fibers for potential application in drywall boards (DB) to address environmental concerns. Six (6) formulations were tested, incorporating rice and banana crop wastes, as well as paper and carton boards, mixed with plaster of Paris binder and perlite powder as fillers. Specifically, the formulations were: P-1 (plaster of paris), P-2 (plaster of paris and perlite), WR (waste paper and rice straw), WB (waste paper and banana fiber), RB (rice straw and banana fiber), and lastly, WRB (waste paper, rice straw and banana fiber). Results showed that formulations containing rice straw and banana fiber (RB) exhibited the most promising thermal properties, with RB outperforming common commercial drywall boards in terms of R-values. RB also showed favorable moisture absorption rates. However, all formulations had higher water absorption rates than expected. The study concludes that RB has potential as an interior drywall board due to its insulation properties and recommends further research into additional properties such as acoustics and fire resistance. Despite water absorption concerns, RB remains a viable option for environmentally-friendly construction materials.