Yup, the lab could tell a difference! Shiney side (so mill roller facing, as opposed to the dull side which faces the other layer of aluminum) was marginally more reflective, but I believe (and a former coworker also remembered it as) it was less than a tenth of a percent (<0.1% for the visual folks)
Anyone who says it affects cooking time or something is mistaken, Iโd wager.
Jokes on you.
I baked my casserole with the shiny side up and pulled it out at 59 minutes and 55 seconds, when it was supposed to go for an hour.
So take that Dull Side!
Any info on surface roughness? Iโm thinking shiny side would be smoother and therefore less sticky, though I donโt know how much the passivation layer would affect it. Probably no where close to making a difference at the end of the day, but Iโm curious.