The invention discloses low dielectric loss cable sheath silicone rubber and discloses a pouring type modified urea resin foaming heat insulation material which is formed by a component A and a component B. The component A comprises phosphoric acid, a foaming agent, foam stabilizer and water. Sodium dodecyl sulfate is selected as the foaming agent, and silicon resin polyether emulsion is selected as the foam stabilizer. The component B comprises urea resin aqueous solution and a crosslinking agent. Polyatomic alcohol resin is selected as the crosslinking agent. In use, the heat insulation material can be obtained by mixed foaming of the component A and the component B. The foaming speed is quick, and the obtained heat insulation material is good in heat insulation effect and high in toughness and can meet the heat insulation material requirements in building industry construction.