Thin metallic films are required to provide interconnection between contacts on devices and between devices. As device dimensions decrease, the low electrical resistivity becomes the most important issue in microelectronics industry. Recently in thin metallic films, hydrogen has been shown to lower the electrical resistivity of thin metallic films, reduce the rate of electromigration in interconnect lines, and lower the stress generated in thin metallic films during annealing. These effects are referred to as hydrogen effects. Low temperature resistivity measurements were performed to determine the effect of hydrogen and temperature on the resistivity of an aluminum-2 wt % copper film. Low temperature control experiments were performed in helium since it has a similar thermal conductivity as hydrogen but is chemically inert. The electrical resistivity of an aluminum-2 wt % copper alloy is lowered by hydrogen even at low temperature. The temperature coefficient of resistivity (TCR) values are identical within the experimental error (+/-0.005 mu Omega cm/K). This means that phonon scattering is identical. So the decrease of the electrical resistivity is due to the decrease in the residual resistivity. Hydrogen effects are reversible for an aluminum-2 wt % copper alloy at room temperature because the adsorption and desorption of hydrogen occur. Hydrogen effects are slowly reversible for an aluminum-2 wt % copper alloy at low temperature because the adsorption of hydrogen occurs, but the desorption of hydrogen does not occur readily.