When I wash my hair and go to sleep, my hair is impossible to comb in the morning, stubbornly sticking to the shape it assumed during the night. The only way to get it right is to wet it again and comb it. What's the cause of this memory effect?
[Physics] Why does wet hair keep its shape when it dries
everyday-lifewetting
Best Answer
Hair, like fingernails and animal horn is made up mostly of a protein called Keratin. The strength and hardness of this polymer is caused by three types of chemical bonds: ionic bonds, hydrogen bonds and disulphide bonds. Water can significantly break the first two types (but not the disulphide ones).
Significantly wetting hair thus leads to making it more flexible and softer. But if wet and deformed hair dries it tends to retain the shape it was in while it was wet. The reformed hydrogen and ionic bonds then leads to a 'permanent' deformation (until you wet it again).