Amazon.com : Pack of 25 11x17 3/16" White Foam Core Backings : Office Products
Standard Carbon Fiber Foam Core Panel — Hillside Composites
Amazon.com: Foam Boards White Foam Core Backing Boards, Silver Craft Knife with Protective Cap and 12 Inch Stainless Steel Ruler for Art Presentations Crafts Display Favors(White, Silver, 12 x 10 x 0.2