The thermal conductivity of nacre from red abalone (Haliotis fulgens) has been determined as a function of temperature (2–300 K), direction, and treatment to partially demineralize or to remove a portion of the organic matrix. The room-temperature thermal conductivity and specific heat of nacre are ∼1 W m−1 K−1 and 0.9 J K−1 g−1, respectively. The thermal conductivity of nacre is rather low and glass-like. It is not as anisotropic as one might expect on the basis of brick-and-mortar structure, in support of recent findings that the aragonite tablets are not monolithic. Partial removal of the mineral component reduces the thermal conductivity in both principal directions, whereas partial removal of the proteins (as observed by 13C NMR) only reduces the thermal conductivity across the aragonite layers.