A systematic experimental investigation of the cryosorption ofH2by cold cryodeposited-CO2frost is reported. It is shown that the sorption capacity of the frost depends upon the conditions at which the frost was formed and its temperature history. Frosts formed in a manner to make them porous or disordered are shown to possess greater sorption capacities. It appears that surface diffusion of absorbed molecules into a disordered frost structure is the basic pumping mechanism. Isotherms forH2sorbed byCO2frosts formed over a wide range of conditions are presented. Also, the reuse sorption capacity of the frost is well documented. As a result of the present tests, it is now possible to put the process of frost-cryosorption pumping into better perspective.