1.Cut 6 pieces of fabric, each measuring 42 cm x 42 cm (seam allowances are included). Sew the four pieces together at the sides to make a ring. Start sewing 1 cm from the top edge. Stop sewing 1 cm from the bottom edge on two of the seams that are adjacent to each other. See fig. 1. Press the seams apart. 
2.Sew the top square on one side where your started 1 cm from the top edge. See fig. 2. Press the seams. 
3.Sew the base square on one side where your stopped 1 cm from the bottom edge. See fig. 3. Mark the middle on the opposite side of where you sewed. Also mark the middle of the side outside of the bottom mark. See fig. 3. 
4.Sew the zips onto the base square. The sliders should meet at the mark. See fig. 4. Make a mark on the zip to indicate the corner and sew the zip at the sides. Adjust the corners and sew the rest of the zip towards the middle. Turn right side out and insert the cube into the cover.
