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
4' x 8' Corrugated Plastic Sheet - 4mm White - TekSupply
Corrugated Plastic Sheets, Sheets 4'x 8', corrugated black sheet, set shop
Coroplast 48 in. x 96 in. x 0.157 in. (4mm) Black Corrugated Twinwall Plastic Sheet (10-Pack) COR4896-BK - The Home Depot