Why do white clothes become see-through when wet?
In: Other
The water both magnifies light like a lens when it exists in droplets, and causes the fabric to cling to skin. These two factors make light colored clothing appear see-through when wet.
I suspect it has to do with scattering of light. A large number of cases of things we view as white are actually clear (at a microscopic level) but the actual physical structure of the object is rough or has lots of holes. As light passes through the object, if it’s smooth, the light passes through or is reflected back all at basically the same angle. If it’s not, light will bounce around in all different directions and “blur” the image until the light is so random it all looks white.
Think of etched glass. We know glass is clear because we see it every day as windows, but when it’s etched it gets that “foggy” white appearance because the surface has been made rough and scatters light.
You can think of a white shirt similarly. The fibers are largely clear but there is technically air space between the weave of the fabric. This scatters the light normally, but when you get the shirt wet it, 1) helps align and keep the fibers together, and 2) fills the gaps with water, which probably has a much closer index of refraction to the fibers themselves, further reducing scattering. Can’t find what that index of refraction is, but suspect it’s similar to other polymers.
Okay, so one answer here is right and the other is far off. The correct answer is light scattering. Thing’s that appear opaque do so because they scatter light in random directions roughly equally. Getting something wet “fills in the gaps” and creates a single “uniform” surface for the light to interact with.
Think that demonstration you see online where someone puts cellophane tape on a frosted window and makes it transparent.
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