The present paper describes the status of a number of studies involving NPL which are directed towards development of internationally accepted reference materials to serve different requirements. These include (1) thermal diffusivity and thermal condustivity measurements on candidate molten metal reference materials; (2) co-operation flash diffusivity measurements on glassy carbon, a dense fine grain alumina, and other ceramics; (3) inter-European studies, one using different steady-state and transient methods to evaluate the properties of a high temperature ceramic and the other using the guarded hot plate method to produce a high temperature thermal insulation reference; (4) a six-laboratory European program to certify a replacement European thermal insulation reference material for use at room temperature; and (5) an intercomparison between standards organizations in five countries on the current reference materials supplied in each country or geographical area. Brief mention is made concerning other on-going and planned work together with recommendations for materials to address additional needs.