Hi, it might be Hooka. My husband smokes hooka and uses aluminum on top of the coals to put the "sheesh". It is legal to buy (tobacco with flavors). It is generally sticky and there are different flavors.
Sadly, heroin is also smoked in foil and if smoked, there is usually long skinny lines on the aluminum. If there are holes in the foil (small pokey ones) and the pieces are small, it might be hooka. either way, watch behaviors. If its pills or heroin, his eyes will be pinprick pupils and he will alternate from being drowsy and soft spoken to very animated.