Smooth, shiney surfaces tend to be reflective but have a very low emissivity value which tends to trap the heat inside. Like chrome tools in your toolbox when you leave the lid open in the sun, a chrome door handle, the ignition switch in your car. Most paints emit in the .92 range regardless of color. The chrome bumper being chrome will reflect most of the radiant heat. However, due to the low emissivity, the heat is trapped and the surface temperature rises.
Aluminum foils are one common material.
Our proprietary products use a new type of plastic radiant barrier made possible by successful research into making a lighter weight radiant barrier for spacecraft. The process is called vacuum deposition technology and it makes it possible to put a very thin deposit of metal on a film substrate. And it remains the hottest place in the attic until the next morning when the sun begins its radiant heating again. It is easy to comprehend when we consider that the insulation has been absorbing radiant heat all day long, and now it is resisting that heat is trying to leave into the cooler attic air and radiating to the cool roof decking. One problematic technique is to put radiant barrier directly on the underside of the roof sheeting.