IEC TR 60076-26: 2020 which is a Technical Report, provides the functional requirements of insulating liquids that are considered necessary for use in power transformers, including, for example, reactors and HVDC transformers, are assembled and listed. A relevance index of importance for design and for service as well as the status of validation is given for all individual requirements (parameters). All parameters are assigned to one of the following categories: General (physical / chemical) Dielectric / Insulation Thermal / Cooling Ageing and Stability Liquid-solid system Material compatibility The document is intended to serve as a general reference document for the transformer industry, including liquid suppliers as well as relevant scientific and technical bodies dealing with insulating liquids (materials).