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How Hair Changes Shape
Heat creates the opportunity for change. A set is not finished until the hair has cooled and stabilised in the intended shape.
This is one of the most memorable, demonstrable lessons of the day. The whole story of styling hair comes down to one idea: heat creates the opportunity for change, and cooling locks it in. A curl is not finished when you take the iron away. It is finished when the hair has cooled and stabilised in the shape you gave it.
The science The science behind it
The bonds (beginner level). Three kinds of bond hold hair in its shape, and only some of them are ours to move day to day.
- Hydrogen bonds are temporary; they are affected by moisture, drying and heat. This is the main everyday styling story.
- Salt bonds are affected by pH changes.
- Disulfide bonds are strong structural bonds, altered by chemical services and not rearranged by normal temporary bridal styling in the same way.
For everyday styling, hydrogen bonds are the bonds we most commonly manipulate, through moisture, heat, tension, drying and cooling.
The set, step by step
Moisture and heat allow reshaping, then tension and direction set the result, then cooling and drying stabilise it, and humidity encourages reversion. Section size, tension and condition all change the outcome. More hairspray cannot rescue a weak structural set.
Why beginners lose the set
The set slips for a handful of predictable reasons: releasing or brushing a curl while it is still warm; sections too large to heat through or to hold; overheating resistant hair instead of diagnosing the real problem; and relying on product to fix poor prep.
Demonstrate live. Compare a curl released and disturbed warm against a curl supported and cooled in shape. Ask students to predict the difference before you reveal it.
- Hydrogen bonds
- Temporary bonds affected by moisture, drying and heat; the main bonds we manipulate in everyday styling.
- Salt bonds
- Bonds affected by changes in pH.
- Disulfide bonds
- Strong structural bonds altered by chemical services, not rearranged by normal temporary bridal styling.
- Temporary set
- A shape created with moisture, heat, tension and direction, then stabilised by cooling and drying.
- Reversion
- The hair returning toward its natural shape, encouraged by humidity and moisture.
- Elasticity
- The hair's ability to stretch and return; it governs how well a strand takes and holds a set.
A curl you set an hour ago has already dropped. You brushed each curl out the moment you released it from the iron, while it was still warm. What is the most likely cause?