Question

paper by itself catches fire easily whereas a piece of paper wraped around an aluminium pipe does not

Answer 1

Because when paper is wrapped around aluminium then the heat transferred to paper by the candle (or whatever is the medium), the heat is transferred to aluminium and thus it doesn't catch fire as we know that to catch fire the body needs to get to its heat

Answer 2

Because papers ignition temperature is more it catches fire easily and when it is covered with alluminium pipe it does not catch fire easily as it's ignition temperature is high