Bookcases are made very sturdy material, including 3/4" thick solid wood face frames and moulding, 3/4" thick furniture-grade plywood sides and shelves, and 1/4" thick furniture-grade plywood backs. The outer layer of plywood is made of the same wood species as the solid face frames. NO particle board is used.

Bookcases 48" or wider require a center divider to provide added stability to the unit and ensure that the shelves will not bow under the weight of very heavy books or objects. Bookcases converted to a hutch (with no bottom) require installation of a fixed shelf for stability. When a hutch is 48"W or wider, there will be no adjustable shelves under the fixed shelf, since they would be too long to provide adequate support.