Observation pension rookie smooth styrofoam balls Civic Mathematician Link
Juvale Small Foam Balls for Crafts (1.9 in, 24 Pack) | Michaels
10X Craft Foam Balls Large Smooth Round Polystyrene Foam Balls for Craft Use - Makes DIY Ornaments, Wedding Decor, Science Modeling,- White 10cm - Walmart.com
100 Pack 1 Inch Mini Foam Balls for Crafts, Smooth Polystyrene Spheres for DIY Decorations, Home Party, Classroom Spheres | Michaels
72 Pieces of 2" Inch Diameter Smooth Polystyrene Foam Balls for School, Arts and Crafts - Walmart.com