Measure the width and depth of the cube using a measuring tape. Cut a square of quarter-inch plywood to these measurements using a circular saw.
Drill a quarter inch hole in each corner of the plywood sheet, using a power drill. Place the holes approximately a quarter of an inch in from the edge of the wood.
Spray paint both sides of the plywood in a color that matches or complements the color of the cube. Paint the plywood outside and on a covered surface. Apply two to three light coats to prevent drips.
Slide the plywood divider into the cube and position it as desired. If you are using multiple dividers in a single cube, position and install them one at a time.
Pass the end of a plastic zip-tie through one hole in the divider. Wrap the tie around the wire cube then tighten the tie. Tie the remaining corners to the cube with additional zip-ties. Cut the excess ends from the ties.