Microencapsulated phase change materials (MicroPCMs) used as thermal insulating coating and fabrics are usually required to have a prominent thermal stability and a lower permeability. MicroPCMs with a prominent thermal stability and a lower permeability were fabricated by feeding an appropriate content of cyclohexane into n-octadecane followed by heat-treatment at a suitable condition. Microcapsules containing 18-19% reserved expandable space are synthesized at 30-40 wt.% cyclohexane in the oil phase, which have a highest thermal resistant temperature -270 degrees C, and a lower permeability, less than 1.2%. The weight loss of microcapsules is mainly attributed to the leakage of n-octadecane from some broken capsules, so improving their uniformity can efficiently enhance their thermal stability and lower the permeability. (c) 2004 Elsevier B.V. All rights reserved.