never lie smoothly against each other. The result is 'fly away' hair, which stands out from the head and looks unmanageable.
     Conditioners, and shampoos with high levels of conditioning agents in them, leave the surfaces of the hair smooth. There is therefore less friction when the hairs are rubbed: hence less static electricity builds up on them, and 'fly away' is reduced.

Moisture content

The moisture content of hair is greater when the atmosphere is moist and humid, and less when the air is dry. The reason why hair 'collapses' in hot, humid atmospheres is summed up by:

    heat and humidity   -> more moisture
                                 -> less static electricity
                                 -> collapse
In dry conditions:
    heat and dryness    -> less moisture
                                 -> more static electricity
                                 -> more volume (body)

When hair is wet the cortex swells and the edges of the cuticle scales tend to lift. The hair surface temporarily loses its smoothness.There is therefore more friction when wet hair is rubbed than when it is dry. This is what can lead to matting and tangles developing during over-vigorous shampooing (there is not greater static charge on wet hair than on dry).
     These tangles are one of the reasons why many children hate having their hair washed, and the problem is easy to avoid.

Hair diameter
The elastic properties of both wet and dry hair are related to the diameter of the hair shaft. The thicker the hair, the more it will tend to resist stretching.

Porosity

In a normal, undamaged hair shaft, very little water can get either into or out of the cortex. This is because the cuticle covering the cortex is intact, and is then almost (but not quite) waterproof. Shampoos do not damage the

Particularly thick, strong hair: the hairs grow densely and each has a wide diameter

cuticle. When hair is permed or tinted, however, the chemicals have to penetrate the cortex in order to react with the keratin inside it. Increasing the temperature, or applying an alkaline lotion, separates the scales of the cuticle enough to allow the chemicals to pass through. After the processing is finished the scales gradually close up again.
     But if hair is processed too many times the cuticle scales may never return to their original tightness and the protection they once offered is lost. The cuticle can also be damaged in the same way by too much blow drying, curling irons that are too hot, and the effects of wind and sun. The hair becomes increasingly porous, and water can then pass in and out of the cortex.
     Over-porous hair is dry, and tends to develop split ends. The damaged cuticle is fragile, and the damage worsens as time goes by. The greater the damage, the more the cortex swells with water whenever the hair is washed, but the more water it loses when it dries. The repeated wetting and drying of the cortex gradually weakens the hair.