Here’s a Tip
The foundation fabric does not show so it is possible to use fabric that no longer appeals to you for that purpose. If it is a bright fabric, use the wrong side of the fabric as the top of the foundation squares so it won’t show through the light fabrics used in piecing the blocks.
Lightweight interfacing also makes perfect foundation material to reduce bulk at seams. To use, purchase 14¼ yards of 20"-wide interfacing.