McCreary 6.50-7.00-8 Inner TubeSpecialty Tire of America aircraft tubes are made of butyl rubber and are made slightly undersize, so they fill fit easily into a new tire. Aircraft-tire plies are made of nylon, and tires will "grow" slightly, in service. The tube will also grow, and will eventually take a permanent set to the (now) larger inside-tire dimension.
If this now-larger tube is later put into a new tire, it may be too large for the inside-tire cavity, with the result that the tube may have folds in it. In service, these folds may eventually wear through and destroy the tube's ability to hold air.
A slow wearing through will result in a slow leakage of air, and the pilot will be alerted to the problem before it becomes too serious. However, if the tube is torn in a particular takeoff, the tire will probably go flat in mid-air, without the pilot having realized what is wrong. Considering the risks in reinstalling a used inner tube, it is recommended that a new tube be installed in a new tire.