I think he's referring to aluminum conductors. Please see NEC 2008.
Table B.310.3 Ampacities of Multiconductor Cables with Not More Than Three Insulated Conductors, Rated 0 Through 2000 Volts, in Free Air Based on Ambient Air Temperature of 40?C (104?F) (For Types TC, MC, MI, UF, and USE Cables) - under column 9 -90 deg. C -ALUMINUM OR COPPER-CLAD ALUMINUM.