An epoxy fillet is a rounded bead of epoxy putty between two plywood parts. The putty is epoxy thickened with silica or microballoons or wood flour. The fillet does two important things. First, it is a structural joint between two parts. Second, the filet creates a rounded corner so that the fiberglass layed over the top of the filet makes a smooth corner bend with no air bubbles. The radius of the fillet is equal too or larger than the maximum bending radius of the glass that will cover the fillet, in general ?”. When done correctly, the two panels, the fillet, and the fiberglass tape become one solid fused component that structurally reinforces the boat. Those taped seams are the true chines, keels and framing of our boats just as in production fiberglass hulls. Those taped seams can be very thick: close to 1” in some cases. Our builders use many techniques to create clean fillets: squirting the filet material out a plastic bag like a pastry piping bag, shaping the filet with tongue depressors, PVC pipes, small plastic spoons etc. See their web sites for pictures.