Bombardier beetles, as their name implies, defend themselves against the potential predators by spraying boiling-hot and corrosive chemicals which are products of an explosive biochemical reaction taking place in the paired organs called reaction chambers (RCs). Why these beetles can withstand the explosive reaction that takes place in their bodies? Knowledge of thermal properties of the RCs will help to shed light on this puzzle. However, the submillimeter dimension and irregular shape of the RCs discourage the traditional methods for thermal characterization. To overcome this challenge, in this paper a method is developed particularly for measuring the thermal conductivity of a material with dimension as small as submillimeter. The measurement results by this method are demonstrated reliable especially for polymeric or organic materials including the RCs of bombardier beetles. The results in this paper not only help to understand the superior thermal insulation of the RC wall but also offer a facile approach to measuring the thermal conductivity of materials in submillimeter scale. (C) 2019 Elsevier Ltd. All rights reserved.