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 and hot too. Insulation is a heat barrier -- it tries to prevent heat exchange between the two sides. Vacuum is the best. Then air. Metals are the worst. ====================
Wetsuits are a great example of how water is an insulator. when the wet suit gets wet, it puts a thin layer of water between the suit and your skin. This layer of water keeps your body heat in, and the cold water out.