The usual adsorbents, such as activated charcoal, zeolite, etc, being granular materials with low heat conductivity cannot in practice be cooled to the temperature of the external bath at pressures below 10 6 tort (1 torr = 133 N m 2) since the heat of adsorption is only removed by radiation and conduction through the residual gas. The limiting residual pressure corresponding to the temperature of the external medium, is therefore not reached. The action of the adsorbent can be improved if a thin layer of it is in good thermal contact with the surface of a metal with high heat conductivity. This condition is attained, for example, by a thin oxide layer on the surface of aluminium. It is some time since the use of such a film for cryopumping was suggested. ~ ,2 According to Tomashov 3 the film obtained by anodic oxidation consists of two layers: a thin dense layer of thickness 0.01 to 0.1/2 adhering to the metal and an external porous layer. The second layer is crossed by a large number c,f capillary channels, the number of which increases on approaching the outer surface of the film, and with a total volume which can reach nearly half the film volume. 4 Oxide films on aluminium are characterized by a strong bond with the bulk metal and by stability when heated. An apparatus shown schematically in Fig. 1 was used for measuring adsorption. The adsorbing element was a 53.6 mm diameter tube of aluminium, 420 mm long, with an oxide film formed on its inner surface. Films of thickness 20 and 100/2 produced by anodizing in a sulphuric acid electrolyte, were studied. The adsorber was cooled in a cryostat, consisting of helium and nitrogen dewars, containing liquid helium (or nitrogen). The adsorbing element was connected to a thermal decoupler by a permanent vacuum seal which stood many heatings to 400°C and coolings to 1.56 K. The gas under study was let in through a valve and its quantity was determined with a micro-burette or by the change in pressure in a known volume of the inlet system. The pressure in the adsorber was measured with a MM 14m inverse magnetron manometer, 5, in the range 10 s to 10 q 3 torr, and with a M I 1 2 8 ionization gauge in the range 10 s to 10 ~° tore Super-high vacuum magnetoelectric cascade titanium pumps were used in the final stages of outgassing and pumping to obtain a sufficiently clean adsorbing surface. The adsorbent was outgassed at 250 to 300°C for 8 to 12 h. After outgassing the vacuum in the isolated absorption container reached 1 2 x l0 q° torr when cooled with liquid nitrogen and ~10 13 torr when cooled with liquid helium. When measuring adsorption isotherms, known amounts of gas were let into the container successively through tube 20 and the equilibrium pressure determined. As the manometer element 5 was at room temperature, the true pressure Ptr in