Air tube is used to feed dry air from a compressor/dehydrator machine (housed in an Exchange or CO) to large pair count copper telecommunication cables. The dry air at a pressure of 70kPa runs along the inside spaces of these cables, for the full length of the cable run. The cables are maintained at a positive air pressure, in order to prevent water entry into a cable, in the event of a cable sheath or cable joint failure point. The air tube has a tough plastic outer jacket, and is lined with a full circle of a thin layer of aluminum. This aluminum layer is a moisture barrier, and prevents moisture entry into the tube, thereby ensuring the contained dry air remains dry, as it is fed to the outdoor, underground cables.