What the heck is tin foil radiant barrier?
Sounds like the junk that was installed as "insulation" when my parents converted the attic of our house into a bedroom when my little sister was born, back in the 1950s. It's efficacy can be summed up in one simple word: "junk."
Maybe so.
OTOH, many folks around here (DFW) have had good results. Given adequate top & bottom ventilation, an attic in the summer goes from, "Heat stroke after 10 minutes" to "Close to outside temperature and can work up there."
For my own part, radiant barrier is Step #2.
Step #1 was tear out old soffit vents under vinyl soffit vents & clear the way. Step #3 is replace the old, non-working attic fan. Step #4 will be prep for blown insulation (plates on top of junction boxes & flagged with 24"+ flags, 24" tall, 12" diam sheet metal cylinders around light fixture boxes, etc.). Step #5 will be R60 blown insulation (fiberglass or most likely cellulose) in the attic, which is 19"-22" deep, depending on the insulation. Current attic insulation consists of ~2.5" of blown fiberglass.
Back in 2003/2004, I made the mistake in going from the yellow shingles that matched the brick to the dark gray that is most popular. The house has never been as comfy in the summer since, and the attic became unbearable. Next time I shingle, I am buying WHITE shingles, thanks.