Sorption isotherms at 300, 500, 750, and 1000°F for Cs in Na were measured on polished Ni, as-received Type 304 stainless steel, polished Type 304 stainless steel, oxidized Zr, and single crystal Al2O3 over Cs concentrations from 46 appm (atomic parts per million) to 0.03 appm. Cesium concentrations on specimen surfaces that had been equilibrated with the Na/Cs solution were determined with a 137Cs tracer. Cesium sorption was reversible, increased with rising Cs concentrations, and decreased with higher temperatures. Nickel and Al2O3 are superior as packing materials for Cs cold traps because of their higher sorption capacities at low Cs concentrations.