What are backer boards in a bookcase?

Backer boards (also called back panels) are thin panels — typically 1/4 in. hardboard or 3 mm HDF — attached to the rear of the bookcase carcass. They provide structural racking resistance (preventing the unit from racking side-to-side), protect wall surfaces, and give a finished interior appearance. Higher-end units use full 3/4 in. MDF backs. OfficeFurniture2go.com specifies appropriate back panels for each bookcase line — call 1-800-460-0858.