WordNet sense 1 (lining consisting of material with a high melting point; used to line the inside walls of a furnace):

furnace lining

WordNet sense 2 (not responding to treatment):

stubborn

WordNet sense 3 (not tractable; difficult to manage or mold):

intractable

WordNet sense 4 (not responding to some influence or stimulus):

unresponsive

WordNet sense 5 (stubbornly resistant to authority or control):

fractious, recalcitrant