The sol-gel adsorbents of water vapor composed of silica and calcium chloride exhibit fairly stable properties during at least one hundred adsorption-desorption cycles, with sorption capacities ca. 1 kg of water/kg of adsorbent. These materials can be regenerated by heating at 200 degrees C. In the relative pressure range 0-0.25 water adsorption can be effectively portrayed using the Dubinin-Astakhov equation. Investigations tend to indicate that the multilayer mechanism of water adsorption, boosted by a synergistic effect of calcium chloride and silanol groups, stands behind the remarkable adsorption properties of the SiO2-CaCl2 composites.