Place folded napkin on 24-inch cord. Loop left side of cord, with loose end over standing part.
Lay right side across loop; slip it under the left side's standing part and then over the loose end.
Bring end of right cord under top edge of loop.
Continue over the standing part of the right side, then under the bottom of the loop. Hold loose ends securely, and gently pull standing parts until the knot forms. Trim loose ends.
Place folded napkin on 18-inch cord. Make a long loop in each side of cord.
Bring loops together in center of napkin.
Tie loops in a knot close to napkin.
Pull the loose cord ends and the loops in opposite directions to tighten. Trim ends to 3 inches.
Lay 18-inch cord diagonally across front of napkin; bring ends straight across behind napkin.
Bring ends to front of napkin. Form square knot by tying two knots, first crossing right end over left (and pulling tight), then left over right.