Bev,
Formica is usually glued to particle board for counter tops--it's usually a very thin, pliable top that comes in several patterns.
I would think if you need a ruler, it would not have enough "lip" on it to successfully guide your ruler. If the plexiglass ones are too expensive, watch for a Joann's 50% off or 40% off coupon and get one then. I did that to get the jumbo Olfa cutting mat.
I also use an old t-square my hubby had--it's metal and used for shop work. It's a great ruler for quilting--very heavy and I also use it to cut wallpaper-- :lol:
HTH,