The reason that fiberglass is a good insulator is principally because of the vast amount of air spaces trapped in it. Heat from the relatively warm ground is conducted by the gravestone to melt the snow in contact with the gravestone. Likewise for trees or any materials that are better conductors of heat than snow, and that extend into the ground. The snow and ice of the igloo is a better insulator than wood. You would be warmer in the igloo than the wooden shack.
Heat is transferred from the hot surface to the air by conduction.
Then convection circulates the heated air, which rises, allowing cooler air to conduct more heat from the earth's surface. Because of convection, considerable heat energy is carried from the earth's surface to high altitude. Much of the energy of the flame is readily conducted through the paper to the water. The large amount of water relative to the paper absorbs the energy that would otherwise raise the temperature of the paper. You can hold your fingers quite close to the side of a candle flame without harm because the air between is a good insulator.