  4$f$ electron-based topological Kondo insulators have long been researched
for their potential to conduct electric current via protected surface states,
while simultaneously exhibiting unusually robust insulating behavior in their
interiors. To this end, we have investigated the electrical transport of the
3$d$-based correlated insulators FeSi and FeSb$_2$, which have exhibited enough
similarities to their $f$ electron cousins to warrant investigation. By using a
double-sided Corbino disk transport geometry, we show unambiguous evidence of
surface conductance in both of these Fe-based materials. In addition, by using
a 4-terminal Corbino inverted resistance technique, we extract the bulk
resistivity as a function of temperature. Similar to topological Kondo
insulator SmB$_6$, the bulk resistivity of FeSi and FeSb$_2$ are confirmed to
exponentially increase by up to 9 orders of magnitude from room temperature to
the lowest accessible temperature. This demonstrates that these materials are
excellent bulk insulators, providing an ideal platform for studying correlated
2D physics.
