I made these a long while back for Rylan, when we were still living in Israel. They are based on the Montessori sandpaper letters. We used them as an early writing practice exercise for him. He is writing on his own now, but he pulled them out the other day and showed them to Damian who enjoyed working with them...head start?
They are a lovely tactile way to introduce letter writing and are very easy to make. I simply covered heavy cardboard squares with contact paper to give it a nice smooth surface, to contrast with the sandpaper letters. I found the lowercase alphabet online to use as a template, and then cut them out of a very fine/soft sandpaper, and glued them onto the covered board. If you do make your own, it is important to make sure you get very soft sandpaper, otherwise it will hurt the fingers. You want just enough to give texture. Actually, after making them, I wished I had used a heavy velvet fabric - still tactile, but a little more pleasant.