The Collaborative International Dictionary of English v.0.48:

Insulation \In`su*la"tion\, n.
   1. The act of insulating, or the state of being insulated;
      detachment from other objects; isolation.
      [1913 Webster]

   2. (Elec. & Thermotics) The act of separating a body from
      others by nonconductors, so as to prevent the transfer of
      electricity or of heat; also, the state of a body so
      separated.
      [1913 Webster]

   3. The material or substance used to insulate from either
      electrical or thermal conduction; as, fiberglass is used
      as thermal insulation in the walls and roofs of houses.
      [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

insulation
    n 1: the state of being isolated or detached; "the insulation of
         England was preserved by the English Channel" [syn:
         insulation, insularity, insularism, detachment]
    2: a material that reduces or prevents the transmission of heat
       or sound or electricity [syn: insulating material,
       insulant, insulation]
    3: the act of protecting something by surrounding it with
       material that reduces or prevents the transmission of sound
       or heat or electricity

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "insulation":
   Jim Crow, aegis, alien, apartheid, buffer, bulwark, bumper,
   color bar, contraceptive, copyright, crash helmet, cushion,
   dashboard, division, dodger, ethnocentrism, exclusiveness,
   face mask, fender, finger guard, foot guard, foreigner, fuse,
   goggles, governor, guard, guardrail, hand guard, handrail,
   hard hat, helmet, insularity, interlock, isolation, knee guard,
   know-nothingism, knuckle guard, laminated glass, life preserver,
   lifeline, lightning conductor, lightning rod, mask, mudguard,
   narrowness, nose guard, out-group, outcast, outsider, pad, padding,
   palladium, parochialism, patent, persona non grata, pilot,
   preventive, prophylactic, protective clothing, protective umbrella,
   quarantine, race hatred, racial segregation, safeguard, safety,
   safety glass, safety plug, safety rail, safety shoes,
   safety switch, safety valve, screen, seat belt, seclusion,
   segregation, separation, shield, shin guard, snobbishness,
   stranger, sun helmet, tightness, umbrella, windscreen, windshield,
   xenophobia