This document covers technical insulation systems of operational installations in industry and the building services, such as pipes, ducts, vessels, equipment and built-in components. The document contains methods for the energy efficiency classification of insulation systems for above-mentioned components with an operational temperature range of -30 °C up to 650 °C. The document addresses plant operators, engineers of operational installations as well as the involved contractors such as insulation contractors and pipefitting contractors. The design of safe surface temperatures for personnel protection is outside the scope of this document. This document also does not apply to heating, cooling and ventilation systems in buildings and does not apply to directly buried district heating and district cooling pipes.