[causi]

It absolutely is not. Thin clothing is bad at blocking UV. For example, a cotton t-shirt blocks 41% of UVA and 40% of UVB. That's like wearing SPF 1.7 sunscreen, i.e., you're getting twenty times the UV exposure you'd get wearing bare-minimum SPF-15 sunscreen.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4414538/

[uncensoredjrk]

I am extremely sensitive to the sun and have NEVER been sunburned through a t-shirt or other layer of clothing. I still think it's a valid defense.

[annoyingnoob]

I've been sunburned through a linen shirt (white color shirt and lightweight).

[m55au]

Did you just take two random numbers from that paper without reading any of it?

Their black cotton shirt blocked >99% of both UVA and UVB and the white one roughly 90%.