Much misunderstanding here of "Radiant" in this context.
Also, R-value really doesn't mean much. If you're interested in this kind of thing, go over to Green Building Talk for some interesting stuff. Understanding "envelopes" (house, RV) is a great life-skill. Convection, conduction, radiation, U-value, and how dumb our houses really are.
Radiant barrier is awesome. It doesn't have much R-value (they are liars) but it is amazing in hot sun, as it reflects 97% of heat from the sun. It's also a good windbreak if sealed properly. It does NOT reflect cold in any meaningful way. You can take a sheet of Reflectix from Home Depot, and put it in a crappy window in blazing sun. You will immediately feel at least a 15* temperature drop, even though it has little insulation value and almost no mass.
A big problem is that the reflective sheet MUST HAVE a ~1/2 air gap on one side, or it won't work. Many large manufacturers are violating this law-of-Physics and selling it with much advertising inaccuracy. Somebody will sue them, and then perhaps they will stop.