Shiny Optical Illusion
A: The honest answer to your question is that it could be both. When the hair is healthy, it has a naturally, satiny sheen and this can be enhanced by wearing an equally shiny fabric. You can also create an equally vibrant enhancement by wearing a matte finish fabric, such as a wool or felted cotton.
So, because your hair needs to be healthy and have its own shine already, the result of wearing a shiny fabric is "coincidental" in that sense. It wouldn't be possible were the hair not already shiny.
However, it is an optical illusion that the hair appears even more shiny and satiny when paired with a shiny finished fabric. The type of fabric you wear on your body has no bearing on the condition of your hair. However, silks and satins offer low-friction and therefore are less likely to cause damage to the hair from rubbing and brushing against the hair.
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See also:
How to get glossy pin straight hair
Causes of dull hair and how to make your hair shiny
How to prevent static hair when wearing nylon clothes
When you have long hair is it better to wear silk and satin blouses?