The effect of coagulation bath temperature on the morphology of wet-spun polyacrylonitrile fibers was investigated by scanning electron microscopy and thermoporometry, a calorimetric technique based on lowering liquid triple point temperature inside the pores. Fibers were fabricated at two coagulation bath temperatures of 5 degrees C and 60 degrees C. The shape of nascent fibers cross-section transforms from bean to circular and pore size increases with coagulation temperature. Porosity parameters including average pore size and pore size distribution, pore volume and internal surface area were determined by thermoporometry. The average pore size and pore volume of the fibers increase with coagulation temperature. Low heating rate of 0.1 degrees C/min during thermoporometry measurements is the key parameter to ensure that test conditions are close to equilibrium. This study shows that thermoporometry can be employed to characterize closed mesa-porosity of wet-spun fibers inaccessible by other standard porosimetry methods. (C) 2011 Elsevier B.V. All rights reserved.