There are newer additives to Al foil to make it nonstick which involves a polymer coating. A plastic, which also helps it burn I suppose.
"Forensic Comparison of Household Aluminum Foils Using Elemental Composition by Inductively Coupled Plasma—Atomic Emission Spectrometry
Koons RD, Peters CA, Merrill RA
Abstract
Inductively coupled plasma-atomic emission spectrometry (ICP-AES) provides the precision, sensitivity, and specificity for element concentration determinations required for good discrimination among sources of household aluminum foil. The concentrations of copper (Cu), gallium (Ga), iron (Fe), magnesium (Mg), manganese (Mn), titanium (Ti), vanadium (V), and zinc (Zn) were determined in aluminum foil by ICP-AES with analytical precisions (rsd) in the 1 to 2% range and nickel (Ni) and silicon (Si) with analytical precisions of about 5%. For these ten elements, the combined analytical uncertainties and variations along the length of a single roll of foil are much smaller than the variations from roll to roll, both within a single brand and across brands."
http://journalsip.astm.org/JOURNALS/FORENSIC/PAGES/1883.htmBeware of this google type of search, you may end up in foils of Barium and such for NASA materials sscientists. It's a futile search nearly.
Andy