Poplar is used for the solid wood on the Paint Grade doors. Poplar is a medium weight and strength wood and very stable. The yellowish color has a slightly greenish cast and occasionally with rather dark streaks. A wide range of color and grain allowed. The Series 100, 400 and 700 flat panel doors have a 1/4" thick MDF center panel. You can request a veneered center panel (it will be Birch) with the Poplar frames. You can request Soft Maple for the solid wood used in Paint Grade doors, call for pricing.