Coroplast Plastic cardboard 0.157-in T x 24-in W x 36-in L Black Corrugated Plastic Sheet in the Polycarbonate & Acrylic Sheets department at Lowes.com
Amazon.com : Corrugated Plastic Sheets | 17in x 13in | 10 Pack | Blank Coroplast Poster Board Signs for Offices, Classrooms, Yard and Garage Sales, Realtor Open Houses, and Custom Birthday, and
Amazon.com : Corrugated Plastic Sheet for Indoor and Outdoor Use - 3/16 Inch Thick Poster Board, 24x36 Inches - Pack of 5 White Plastic Board Sheets - Waterproof Coroplast Sheets and Lightweight
Corrugated Plastic Sheets, 26 x 62", Black for $21.03 Online | The Packaging Company
Corrugated plastic Polycarbonate & Acrylic Sheets at Lowes.com