Insulation material used to surround process pipes and process vessels to reduce heat transfer. The properties of the insulation material are a low thermal conductivity and effectiveness at minimizing heat transfer, cost, and durability. It should also be corrosion-proof, water and weather-proof. The correct thickness of lagging should be determined based on economics. There is an optimum thickness of lagging for pipes and it is a balance in cost between thickness and surface area which increases with increasing thickness.