To provide a moisture retention material obtained by using a solid component of a micro capsule containing a thermal storage medium that has functions to remove various uncomfortable odors derived from materials for the thermal storage medium and those necessary for microcapsulation and as heat generating materials having quick and stable temperature reproducibility by microwave when heating the microcapsule containing the thermal storage medium and a composition containing a water absorbable pigment by irradiation of microwave.

A composition containing the solid component of the microcapsule containing the thermal storage medium, a monolithic carbon compound and/or the water absorbable pigment with 3-60% of water absorption rate is used as the moisture retention material. It is favorable that the monolithic carbon compound comprises an activated carbon and the water absorbable pigment comprise silica gel, magnesium silicate, activated alumina, or zeolite. The moisture retention material is heated by irradiation of microwave.