Please help, unsure of how to finish this pattern… Sewing Machines Parts and Sales in Los Angeles

Hello. I recently inherited some old fabric and patterns, and included are six triangles, which are clearly intended for a specific purpose. The original seamstress has passed, and I am unsure what her intent was for these triangles.

They are each double layered, or lined perhaps, with the bottom edge left open. The other side of the cloth is a plain lightweight fabric, and the patterned side is shiny with a vinyl-like quality. I am fairly new to sewing and I have no idea what these were meant for. I would like to finish whatever she was planning on doing with these triangles. I have a lot more of the same cloth as well, implying it was a larger project. Does anyone have any ideas?

Thank you very much.