RELIABILT 1/2-in x 6-in x 4-ft Square Edge Unfinished Poplar Board in the Appearance Boards department at Lowes.com
Yellow poplar | The Wood Database (Hardwood)
WoodSense: Spotlight on Yellow Poplar
Poplar Lumber Board (S4S), Solid, Hardwood - 6 in x 3.5 in x 0.75 in (Actual Size) - Finished on Four Sides - USA Source - Great for Small Home Projects and Renovation - - Amazon.com