Foam Core Backing Board 3/16" White 30x40- 50 Pack. Many Sizes Available. Acid Free Buffered Craft Poster Board for Signs, Presentations, School, Office and Art Projects - Walmart.com
Amazon.com : Union Premium Foam Board 30 x 40 x 3/16" 10-Pack : Matte Finish High-Density Professional Use, Perfect for Presentations, Signboards, Arts and Crafts, Framing, Display (White, 30x40) : Office Products