The thermal diffusivity and specific heat of Armco iron are reported in the temperature range of 25° to 1000°C. Electrical‐resistivity values are reported from −272° to 1000°C. The thermal‐diffusivity values as measured by several different methods on the same material are compared. The thermal conductivity is calculated from the thermal diffusivity and specific heat and compared with values reported from direct measurements by other investigators. These measurements were carried out as a contribution to a cooperative program for the characterization of Armco iron as a high‐temperature thermal‐conductivity standard. Armco iron appears to be a satisfactory thermal‐conductivity standard, with an error of 2% or less, from 25° to 700°C; above 700°C the thermal history of the iron sample becomes important and iron is less satisfactory as a standard. Reproducible values above 700°C may still be obtained, but only if the sample has had adequate heat treatment.