I have used Carol Doak foundation paper and like it a lot. I have also used copy paper and find that the cheaper, the better for this purpose. I know there are people who like freezer paper but I found that it is not flexible, does not fold as cleanly and hard to tear away and stretches the thread in the stitches. My first consideration is that it go through the printer without hassle. The second is that it tear easily and quickly. I really enjoy paper piecing because of its precision. It is its own 'journey'.