tin or metal
Yes, because it does not conduct heat.
Concrete is one of the worst insulators
Non-metal
yes it is a conductor because today we can get hot water and cold water it can be dirty or clean.
lava
Insulator
Depends what's in your gravel. In order of best to worst: Sandstone 1 Limestone Concrete Water Soil ref:http://en.wikipedia.org/wiki/List_of_thermal_conductivities
pure water is an insulator.
Air is the worst sound insulator as it allows sound waves to pass through easily. Materials like foam, fiberglass, or mass-loaded vinyl are better options for soundproofing.
To isolate hot terminals
Yes it is a insulator and NOT a conductor
is water conductor or insulator