Combustibility of Paper
Paper is highly combustible because it is made from cellulose fibers which are easily oxidized. When exposed to heat or flame, the cellulose fibers break down and release flammable gases like carbon monoxide and methane, which can ignite and sustain a fire.

Insulation and Heat Transfer
When a piece of paper is wrapped around an aluminum pipe, the aluminum acts as a heat conductor and draws heat away from the paper. This heat transfer prevents the paper from reaching its ignition temperature, thus protecting it from catching fire.

Heat Dissipation
Aluminum has a high thermal conductivity, meaning it can quickly dissipate heat away from the paper. As the aluminum pipe conducts heat away from the paper, the temperature of the paper remains below its ignition point, preventing combustion.

Physical Barrier
The aluminum pipe also acts as a physical barrier between the paper and the heat source. This barrier prevents direct contact between the paper and the flames, further reducing the risk of ignition.
In conclusion, the combination of heat conduction, heat dissipation, and the physical barrier provided by the aluminum pipe prevents the paper from catching fire. This demonstrates the importance of understanding the properties of different materials and how they interact with heat to prevent accidents and ensure safety.