Here's another approach to making a Rekenrek. Used cardboard when I made mine, but I think foam is a great idea! (I too used pipe cleaners and pony beads!)
Quick and easy way to construct rekenreks.
Rekenreks are one our favorite math manipulatives to help build number sense in Kindergarten!
Nasco’s Rekenrek Classroom Kit ~ Rekenreks ~ Counting, Sorting, Place Value