Curling irons are hair styling tools used to create curls in hair. They consist of a heated metal or ceramic barrel that is used to wrap sections of hair around, creating curls or waves. The heat from the barrel causes the hair to temporarily reshape and hold the curl until it is either brushed out or washed. Curling irons come in a variety of sizes, typically ranging from 3/8 inch to 2 inches in diameter. The size of the barrel determines the size of the curl created, with smaller barrels producing tighter curls and larger barrels creating looser, more relaxed curls or waves.