To be fair we need to look at the average cooling energy reduction data points, not just peak.
Radiant barrier (where thermostat temp was left unchanged between seasons): 19.7%, 11.3%, 16%, 27.2%, 5.3%, 8.4%, 0%.
Reflective white roofing: 18.5%, 21.5%, 24%.
Those two studies can't be used to compare the validity of both methods. The study on radiant barriers was performed on actual homes with people living in it with various insulations levels (R-9 to R-30) and ducking systems. The roofing study used 6 identical test homes.
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