Which category of waves works by being processed without heat to achieve a curl?

Cold waves are the correct choice because they are designed to create curls or texture in hair without the application of heat. These waves utilize a chemical process that relies on a specific type of waving lotion or perm solution instead of heat rollers or thermal methods. This allows for the treatment of hair that is more damaged or delicate, as it minimizes the risk associated with high temperatures.

Cold waves generally contain ammonium thioglycolate, which helps in breaking down the disulfide bonds in the hair structure. Once these bonds are broken, the hair can be reshaped and set into new patterns as it is neutralized, resulting in curls or waves. The absence of heat in the curling process allows for more versatility and reduces potential damage to the hair.

Other categories, like true acid waves, chemical waves, and heat waves, involve heat or specific chemical reactions that require temperature to activate and properly shape the hair.