I have a plastic pith helmet. And I was wondering if UV rays can penetrate through the plastic and get on my skin. I hold it up to the light and most of the light doesn't make it but you can see a little light spots. It's kind of thick plastic, maybe a tad bit thinner than a hard hat but about the same thickness as a construction helmet. Maybe just half a millimeter thinner.
Just about all plastics are formulated with UV absorbers built in, because polymers break down so rapidly without them. This makes everyday objects like your helmet last a long time, even when exposed to direct sunlight. Without these absorbers, the plastic would become faded, discolored, and brittle after a very short time. Because of these additives, and because the plastic is relatively thick, no UV rays will penetrate the helmet. It is interesting to note that this UV protection is built into clear plastics as well. So that something like a plexiglass window, which lets in plenty of visible light, will still block out 99+% of the Ultraviolet light that hits it. So the UV protection is there, whether you can see through the plastic or not. The blocking is described in terms of % blocking, rather than UPF which is used exclusively for sunscreens designed for use on skin (even though many of the same UV absorbers are used in sunscreens and in plastics).
