Why does aluminium foil have a shiny and a dull side?

Should You Use the Shiny or Dull Side of Aluminum Foil? – LifeSavvy

You're using aluminum foil wrong: Here's how to use it right - The Jerusalem Post

Fish N Pig - Ah the ago old debate about tin foil. Does the shiny side cook food faster than the dull side? In theory, the shiny side would reflect more heat

Why is Aluminum Foil Shiny on One Side?, by Harlan Brothers

These Aluminum Foil Uses Are Not Advised

When using aluminum foil, does the orientation of the shiny side vs. the dull side matter? - Quora

826: Aluminum Foil - The Shiny vs Dull Side — JC

Aluminium Foil, which side up? Shiny IN or OUT? - Warren Nash

Mistakes You Should Avoid Making With Aluminum Foil

Shiny vs. Dull Side of Foil: Which Should You Use?

Why Aluminum Foil Is Shiny On One Side While Dull On The Other?