Ever wonder what the difference is between foil’s dull and shiny sides? The answer from Alcoa, maker of Reynolds Wrap, which accounts for 60 percent of all aluminum foil sold in the United States: It’s a coincidental by-product of the manufacturing process. “There’s so little difference in heat reflectivity that it doesn’t matter which side is up,” says senior home economist Pat Schweitzer (of Pat-and-Betty fame in the Reynolds TV commercials). She points out, though, that with Reynolds Wrap Release nonstick foil, food always needs to sit on the dull side.