FWIW: From years of experience:
Prior to fabricating a muffler shield to reduce Model A floor board heat ...... if one were to ever experience the difference between standing under a sheet metal roof at noon provided in galvanized steel and standing under another sheet metal roof in aluminum .... the next muffler shield for "experienced" people would be fabricated with aluminum as opposed to steel.
Hot mufflers are producing radiant energy similar to the sun's energy which can easily penetrate wood floor boards and steel ....... also penetrate asphalt shingle roofs, slate roofs, clay tile roofs, and bituminous membrane roofs.
If one researches "radiant barrier insulation" one finds that aluminum provides about 97% reflection of radiant heat, (radiant energy), and provides low-E, i.e., 97% radiant energy emissions when aluminum is not facing the heat source, but is adjacent to at least a 3/4" air space.
Aluminum only reflects 97% of the radiant energy if the aluminum has at least a 3/4" air space on one (1) side of the aluminum. If aluminum is sandwiched between (2) layers of adjacent carpet, or wood, or floor mats, with no air space on one or both sides, reflection of radiant energy is 0%.
Aluminum faced sound deadening material covered with floor mats or similar material, with no air space adjacent to the aluminum facing reflects 0% of radiant energy.