The present study aims to investigate the feasibility of bryophytes plantations applied in extensive green roof in Taipei metropolitan area by measuring the physical properties of water and thermal characteristics of plants, it is expected as a new option of green roof for the Taipei metropolitan area after the promotion activities. Two phases are included in this study. The first phase is to explore the physical properties of water bryophytes. According to previous studies, it was found that the characteristics of Racomitrium canescens is drought-tolerance bryophytes which was proper for the study, in addition to random collection of bryophytes from Taiwan, Racomitrium canescens from Japanese, Sedum mexicanum and Duranta repens Linn. and so on. Above seven plants were the research materials for analyzing their needs of water and differences of the drought tolerance. Racomitrium canescens was regarded as insulation materials in the second phase analyzing its insulation effects by measuring thermal conductivity (k) from the experiments of applying Hot Disk thermal analyzer and means of the chamber-heat flow meter method. The original study was designed to set the standards of drought-tolerance bryophytes by its water content of plant and water potential utilizing the characteristics of non-vascular plants, but it failed to calculate relative water content of above plants, it was required to perform further plant physiology experiments, such as the measurements of chlorophyll fluorescence, free proline, soluble protein content , superoxide dismutase, peroxidase and so on. Thermal conductivity (k) indicates the capability of thermal insulation and the performance of insulation materials, the higher its value means the stronger capacity of heat transfer, therefore material which has the lower value is more suitable for insulation. Thermal conductivity that moss mat of Racomitrium canescens measured by Hot Disk thermal analyzer were 0.06 W/m•K for thanatosis (0%water content) and 0.32W/m•K for non- thanatosis (100% water content) which indicated the insulation capacity of thanatosis is about 5.3 times to non- thanatosis. Thermal conductivity that module tray of Racomitrium canescens measured by means of the chamber-heat flow meter method were 0.23~0.41 W/m•K when water content was 0% and 0.25~0.61 W/m•K when water content was 100%. The order of highest changes rate of thermal conductivity was low-temperature high-humidity environment, thermal conductivity of 100% water content sample is 1.5 times to 0 % water content sample. The second was standard simulation environment, thermal conductivity (k) of 100% water content sample is 1.1 times to 0 % water content sample. The last was high-temperature high-humidity environment, thermal conductivity of 100% water content sample is 1.08 times to 0 % water content sample. "Water" is regarded as the main factor that impacts the plant thermal conductivity. Air changes came from water evaporation due to condensation and water content in porous medium caused the increase of thermal conductivity. Factors of thermodynamic properties impact thermal conductivity are dry bulb temperature (Tdb), specific volume (SV), water enthalpy (Hf), enthalpy of vaporization (Hfg), saturated vapor pressure (Pws) and air vapor pressure difference (VPD). Climate changes can’t be alternated. However, the insulation capacity of green roof could be improved by the structure design and engineering methods of Racomitrium canescens which cause the decrease of thermal conductivity. Proper selections and designs of the storage/drainage layer, the waterproofing membrane layer, the filter fleece layer, the growing media on the substrate structure without interference of the growth of Racomitrium canescens and the thermal conductivity, moisture transmission coefficient, pore characteristics, density, granularity, and directional textures of insulation materials should also be considered. According to the experimental results, the thermal conductivity that moss mat of Racomitrium canescens and module tray of Racomitrium canescens are higher than the general inorganic thermal insulation materials, but the insulation properties of moss mat of Racomitrium canescens and module tray of Racomitrium canescens are poorer than the building insulation materials, it is superior to other materials in the applications of green roof since its lighter load, easier engineering requirements of waterproof protection and maintenance, etc. Racomitrium canescens is a better choice of extensive green roof than other species. The genus Racomitrium (Grimmiaceae) is considered as an option of developing projects of green roof, though there is any commercial plant products for green roof in Taiwan. All products are imported from Japan，thus it may become a potential item in the future.