Head-to-head performance comparisons of the two products indicate specific testing variables (e.g., relative humidity, thickness, or fastener types and spacing) may produce results favoring one material over the other;15 however, in general terms, it is reasonable to use the voluntary performance standards as a mechanism for evaluating the “real world” equivalency of the two products. If either material will significantly exceed the desired minimum level of service and structural performance, then it appears the project designer and specifier need only evaluate nonperformance factors (e.g., cost and availability) before specifying the sheathing system.