Abstract: The 2D barcode at the base of a sample tube is protected from frosting by an air pocket within a wall of high thermal conductivity material that surrounds the barcode. The wall is of thermal conductivity greater than 14W/m K and preferably greater than 200W/m K. The wall may be formed as a skirt extending from the base of the sample tube or as a part of a supporting rack. The wall, cooled by the sample tube and the frozen sample within the tube, collects frost that would otherwise collect on the 2D barcode and deflects the flow of moist air that would otherwise flow against the barcode.