Cut two pieces of 1/4 inch foam board to the length of your basket using the ruler and utility knife. Cut two more pieces to the width of your basket. Cut all of the pieces to the height of your basket.
Use the pencil and ruler to draw a straight horizontal line across the middle of each foam board.
Measure 2 inches in from both outside edges on both sides of each board along the horizontal line. Draw a vertical line down from each of these four points.
Use the utility knife to turn each of the vertical lines into a 1/4 inch groove so that the boards can interlock.
Slide the grooves of the length pieces into the grooves of the width pieces. This interlocking set of dividers should fit firmly into your basket.
Customize your dividers to fit the design of your basket by unlocking them and painting or applying adhesive-backed fabric.