Graphite felts are often activated thermally before use in electrochemical reactors. This has the effect of improving wetting and decreasing charge-transfer resistance. In this work examination is made of the range of properties that arise within two different production charges of the same material from a single supplier. Although, it is clearly critical to know the variance within a single activated felt in order to make a fair comparison among different types of felt, this has been overlooked in previous such studies. Considerable variations were observed between two polyacrylonitrile (PAN) based felts from different production charges after thermal activation, despite both charges being of the same type of felt from one supplier. Particularly, one charge of felt lost considerably more mass and increased more in electrical double layer capacitance, on activation at a given temperature, than the other. To understand the cause of these differences the felts were examined as supplied and then after heat treatment over a range of temperatures. In the first part of this study the physical and morphological aspects of the felt are explored, before and after activating at temperatures of up to 575 degrees C in air. (C) 2015 Elsevier Ltd. All rights reserved.