Abstract The room-temperature thermal diffusivity of high T c materials is dominated by phonons.This allows Mud Flap the scattering of phonons by electrons to be discerned.We argue that the measured strength of this scattering suggests a converse Planckian scattering of electrons by phonons across the room-temperature phase diagram of these materials.Consistent with this conclusion, the temperature derivative of the resistivity of strongly overdoped cuprates is noted to show a kink at a little below 200 K that we argue should be understood Plug and Play Remote Starter as the onset of a high-temperature Planckian T-linear scattering of electrons by classical phonons.This kink continuously disappears toward optimal doping, even while strong scattering of phonons by electrons remains visible in the thermal diffusivity, sharpening the long-standing puzzle of the lack of a feature in the T-linear resistivity at optimal doping associated with the onset of phonon scattering.