Smart textiles are materials and structure that sense and react to environmental conditions or stimuli, such as those from mechanical, thermal, chemical, electrical, magnetic or other sources. The Phase Change Materials are those which change their phase from solid to liquid upon heating and back to solid from liquid when temperature is drop down. During their phase change from Solid to liquid they absorb, distribute and store the heat, and release it when going a phase change from liquid to solid. Thus it keeps the wearer skins temperature constant by absorbing the excess heat and releasing it when required. PCM possesses the ability to change their phase with a certain temperature range, which can be controlled by choosing the various phase change material according to the end use of the product. This paper discuss about the principle of Phase Change Material, Its different type available. The different technology used for the incorporation of phase change materials into textile substrate and their application with limitation is been discussed.