Question

is the expansion of a substance due to heat.

Answer 1

when you heat a substance, the molecules move away from each other, causing the expansion.

Answer 2

...if it is not a rubber band

Answer 3

why do you think that?
you heat a rubber band until its merger and maintain a constant temperature, you will notice that the area occupied is larger

Answer 4

Not necessarily! Water through 0 to 4 degrees Celisius compresses as well as ceramic compound ZrW2O8 when it is heated from 0 to 1050 Kelvins.