Why do certain brands of aluminum foil have a hechsher?

Does aluminum foil or different paper products,  do they need an OU? I'll divide this question   into two parts. One is, should you buy it with  the OU? And one is, if I didn't use the OU,   can I still use the food? In terms of why a person  should get the OU, aluminum foil is made with   oils. There are lubricants that are added to the  aluminum. When they initially make the aluminum,   they make it into a very fine thin roll. There  are lubricants added. Often times these are   vegetable oils. Therefore, it is appropriate to  have a hashgacha on it. If you bought an aluminum   foil without a hashgacha, so there are actually  Teshuvos written about this topic, and most poskim   are lenient for various reasons. Aluminum foil  now, it's been more than 24 hours obviously since   it's been made. Therefore, we assume that the oils  become what we call ta'am lifgam. They give an off   taste, they don't improve it anymore, and  therefore, if a person did use aluminum foil that   didn't have a hasgacha, the food is acceptable but  it is best because there are vegetable oils used   to buy one that has hashka. Similarly with paper.  Paper in general is fine, but there are sometimes   release agents. Let's say on a parchment paper  could have different ingredients that are added   like a coating in them. Things like stearic acid  could be very kosher sensitive, and therefore,   in the first instance, it is best to buy one that  has a kosher certification. If you used one used   one that did not, there's reason you could be  lenient to assume that either the ingredients   were not problematic or the taste will not  affect it after it's been more than 24 hours.