Cooled Hair Before Dressing It
A: I’m going to presume that you are referring to the ‘cooling stages’ after the hair is dried under a hooded dryer, or the act of allowing the hair to cool after being treated with a thermal tool such as a curling iron, before being brushed or combed through.
You see, styling the hair involves breaking the side bonds in the hair, which are what tell the hair what “shape” to fall in. There are chemical side bonds and two types of physical side bonds. It is the physical side bonds that we work with when we perform standard styling techniques. These physical side bonds are hydrogen bonds and salt bonds, each of which can be broken using the application of heat and/or moisture.
This is why curling irons can curl the hair, and why wet sets work also. The hair can be wrapped around a heated appliance (or wet and wrapped on a roller) for a few seconds with a styling product, then the reshaped lock can be allowed to cool (or dried thoroughly and cooled) and the curl sets into place and can be combed through.
If we attempted to “dress” the hair – meaning comb through it and finish the styling - before it was returned to its normal temperature, we would quickly find that we simply pull the curl out of the hair, leaving it straight again. Although if the process we used was designed to straighten naturally curly hair, not allowing the hair to fully cool before further manipulation can encourage the hair to revert to its natural curl.
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See also:
What is hair made of and how does it grow?
What are the physical effects of blow drying on the hair structure?
Can I style newly-permed hair?
Is hair easier to style washed or unwashed?