the present invention is a container assembly that includes an inner tube formed from a plastic that is substantially inert to bodily fluids and an outer tube that is formed from a different plastic . collectively , the container assembly is useful for providing an effective barrier against gas and water permeability in the assembly and for extending the shelf - life of the container assembly , especially when used for blood collection . the outer surface of the inner tube and / or the inner surface of the outer tube are provided with a matte finish that forms an array of peaks and valleys . the valleys form circuitous paths that accommodate a flow of air to facilitate insertion of the inner tube into the outer tube . the circuitous paths also allow air to vent during processing to low pressure .