Stiff unabsorbent napkins
The reason isn't apparent until you see that another use overrides the need to wipe your mouth. Brazilians always pick up sandwiches, cakes, and fried foods like coxinhas with paper napkins, whereas Americans would use bare hands or a fork. Soft American-style paper napkins would stick to the food, especially to the fried food. The crinkly and waxy Brazilian napkins don't stick.
Brazilians will think you strange if you eat with your fingers foods that are often eaten with fingers in the US or Canada. A friend picking or sampling food off your plate in the US or Canada might be annoying behavior, but it really annoys Brazilians.