Carbonated beverages "go flat" / lose their carbonation over time as CO2 that is dissolved in the beverage diffuses out of the container, thereby escaping the liquid beverage. Which diffusivity (also called the diffusion coefficient, D) would you expect to be higher at, say, 25°C?

a. CO2 through aluminum (a very common metal for beverage cans).
b. CO2 through polyethylene (PE, a very common plastic, eg gallons of milk are sold in PE containers).
c. CO2 through steel (a less common beverage container these days).