The lowest or basic strength of aluminum and each of its alloys is determined when the metal is in the annealed or soft condition. This is designated as the O (letter O) temper Annealing consists of heating the metal to the appropriate temperature for the correct period of time. All alloys can be annealed. All alloys also are strain-hardened and strengthened when cold worked, as in foil rolling. When the final product is wanted in the soft condition, it is given a final anneal. Because aluminum and certain of its alloys are strengthened beyond their basic strengths only by strain hardening, they are non-heat-treatable. Nearly all of the foil presently produced is rolled from non-heat-treatable alloys, which are given “H” number temper designations for the various specific strain-hardened conditions in which they are made. For example, common foil availability is alloy 8011-H18; the H1 means strain hardened, and the next digit indicates the degree of hardening, the 8 meaning ful hard.