We're using them up faster than they are made. These natural resources-including forests, coal, and oil-either do not replenish themselves or do so much more slowly than they are consumed.
Like the down on a goose, it's a protective layer against the elements. Technically, insulation is any material that resists the transfer of heat, cold, sound, electricity, and other forms of energy; good insulation is an important part of an energy-efficient building envelope.