Flat panel material will depend if it is interior or exterior use.
- Interior use flat panels : 3/4″ can be solid wood, 1/2″ can be solid wood, anything less than 1/2″ MDF core with veneers.
- Exterior use flat panels : For 2-1/4″ doors 1″ or 3/4″ panels – Extira core with thin veneers.
NOTE : For 1-3/4″ doors 3/4″ panels preferred. Extira core with thin veneers. We have used 1/2″ flat panels with Extira core and thin veneers.
Exterior Exceptions : Knotty Alder, Knotty Pine (any rustic wood) – Use two 3/8″ thick panels face laminated. The veneers for the knotty wood (rustic) do not work well for laminating.
Posted by 
Good's Millwork SOPs 