Good question, Janet. Yes, you certainly can do stitch-and-flip without a foundation, but I find it easier to use a foundation for two reasons: (1) the foundation fabric stabilizes the block and helps keep it flat as you’re working on it. This is especially helpful when you are sewing small pieces. (2) The foundation provides a template that helps you see how big it will be when finished and choose the right size pieces to add. It also helps making squaring up the block easier when you’ve added all the fabric you want.

The downside is that foundation fabric makes the eventual quilt heavier.

In the end, it’s a matter of preference. If you like sewing this block better without the foundation, I won’t call the quilt police on you!