Former Duct insulation which was constructed with glass wool board had two issues : cost and hygienic problems. It was uneconomical due to the labor costs upon construction and material costs (minimum of 25,, thickness required). On the other hand, Rubber Sponge Duct insulation, which is manufactured with synthetic rubber 'Rubber Sponge', is fire retardant treated, light in weight and flexible. It retains low thermal conductivity despite the reduction in thickness(10mm), and has wide range of heat resistant temperature(from -40℃ to 120℃)