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