The hardened concrete's conductivity k_u combines the aggregate, the paste and the air by the rule chosen. In young concrete conductivity is higher while the mix still holds free water and falls as it hydrates, k(α) = k_u(1.33 − 0.33α) — the form the thermal analysis uses. Specific heat is the mass-weighted mean of the constituents, with water bound by hydration counted at its lower heat capacity.

Conductivity measured at several ages, each with the specimen's curing temperature. Ages are converted to equivalent age, the degree of hydration comes from the hydration parameters below (from the Heat of Hydration tool), and k_u is fitted to k = k_u(1.33 − 0.33α).