California Code, Public Contract Code - PCC § 3002

(a) For purposes of subdivision (b) of Section 3400 and subdivision (a) of Section 10129, for any roof project, a material, product, thing, or service shall be considered equal if it meets all of the following requirements:

(b) A substitute may be unequal if the resulting roof system would be substantially different than other equal or better systems in terms of performance and durability, but not merely different by virtue of the inclusion of proprietary products or a proprietary warranty.