> dirt isn't very insulative Whether it is sufficiently insulative depends on the scale of the system. The thermal time constant of a 3D mass is proportional

> dirt isn't very insulative Whether it is sufficiently insulative depends on the scale of the system. The thermal time constant of a 3D mass is proportional to (thermal conductivity)^-1 (heat capacity per volume) (radius)^2. So if the thermal conductivity is too high, just increase the size.