There are various kinds of permanent waves that yield different results. Curly or spiral perms produce tight, spiral-shaped curls and usually looks best when the hair dries naturally or is dried with a diffuser. Body waves produce looser curls and add volume and fullness. The tightness of the curls depends on the shape and size of the rod that the hair is wrapped around. It's important to research all of your options before deciding which permanent wave is right for you. Permanent waving solutions work by penetrating the cuticle and breaking down the bonds in the cortex, causing the hair to give up its original shape and conform to the rod that it's wrapped around. A solution called a neutralizer is then applied to reform the bond, helping the hair hold the new curl. However, not all perm solutions work the same way. Cold wave perms work through chemical action alone to produce the longest lasting results. Acid perms, the most widely used, work in combination with heat and are gentler than cold wave perms, but they tend to relax more quickly. In addition, there are permanent waving formulas for different types of hair, special formulas for color-treated hair, and soft perms for in-home use.