According to StraightPerm.com, a Japanese straight perm is a thermal reconditioning process that uses hair products and a special straightening iron to create straight hair. It does not use the kind of chemical relaxers used in some other straightening processes.
Japanese straight perms cannot be performed on all chemically treated hair, including some hair that has been bleached, highlighted or relaxed. A hair stylist experienced with straight perms can determine whether someone's chemically treated hair can be straightened. The straight perm process works best on hair that is at least 8 inches long. After a Japanese straight perm, the hair is allowed to air dry with perfectly straight results, but can still be styled in any manner.