A simple adiabatic calorimeter has been built to investigate the heat capacity of small (<= 1 cm(3)) samples of carbon nanomaterials at temperatures ranging from 1 to 300 K. It enables (i) rapid mounting of samples (ii) doping of samples with gases directly in the calorimeter, and (iii) rapid cooling of samples to liquid helium temperatures. It can be placed in the helium vessel of a portable Dewar or in a helium cryostat. The heat capacity of a fullerite sample is measured in the temperature range 1-30 K. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3605700]