The four natural metals with the highest infrared reflectivity are aluminum, copper, silver, and gold. Recent technological breakthroughs at Sigma Technologies allow copper to be deposited and coated at a very reasonable price, allowing us to make a superior radiant barrier.
Gold is 97.5% reflective and naturally resistant to corrosion, but is too expensive to be realistic.
Silver is 98% reflective but is less corrosion resistant than gold and still not cost-efficient.
Copper is 98% reflective, has excellent corrosion resistance, and is considerably less expensive.
Aluminum starts at 97% reflective but corrodes easily when exposed to heat and humidity.
What is Corrosion
Not all metals maintain their reflectivity. Many metals corrode in the presence of heat and moisture. When exposed to steam or liquid water, the reflectivity of aluminum can drop to 50% reflective. Copper is considered a "noble metal" and is naturally corrosion resistant.