There are lots of colour treated hair facts out there. One of the most well-known is that women often notice that their hair feels thicker after hair colouring, especially those with fine hair. In reality, the hair colouring process does not make hair fibers physically thicker but it can make hair fibers rougher, which can create the appearance and feel of thicker hair.
This is because the rougher texture causes neighboring hair fibers to “grip” each other rather than slide past each other the way smooth fibers do, which can prevent hair from falling flat and make it seem fuller. This perception of thicker hair is one of the great colour treated hair facts that is (somewhat) true.