AbstractA low-cost sepiolite (SEP) was used to replace wheat flour (WF) as a filler applied to melamine-urea-formaldehyde (MUF) resin. Three-ply plywood was fabricated with different SEP/WF formulations, and its wet shear strength and formaldehyde emission were tested. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to explain why the performance of the plywood improved. Results showed that the wet shear strength of the plywood increased with the addition of SEP in the filler. When using SEP to replace 80% of the WF, the wet shear strength was improved by 27.8%, which was attributed to the penetration network with hydrogen bonds formed by SEP and MUF resin. Using SEP in the filler formulation created a smoother, denser, and more regular cross-section to prevent moisture intrusion, which improved the water resistance of the adhesive and thus further increased the wet shear strength of the resultant plywood. The tunnel structure of SEP could accelerate the free formaldehyde emission of the plywood. As a result, using SEP replace 80% WF as a filler, the formaldehyde emission of the plywood was reduced by 7.8% due to the tunnel release effect.