An insulation board for a resistor grid and methods for manufacturing the same are disclosed. The insulation board consists of a plurality of longitudinal voids. One or more longitudinal structural members are disposed in the longitudinal voids. The longitudinal structural members may be shaped to conform to the shape of the longitudinal voids. The method of constructing the insulation board includes providing a profiled block and inserting one or more longitudinal structural members in the longitudinal voids. Alternatively, the insulation board may be constructed by providing one or more longitudinal structural members and molding a profiled block over the longitudinal structural members. One or more rows of transverse pin holes may be provided along the length of the insulation board for engaging pins of resistive elements of the resistor grid.