Very special fabric - Marino wool. If you look at the manufacturers website, they have a silly challenge where you can wear this shirt for 100 days in a row, and it still won’t stink because the fabric is antimicrobial. I haven’t done the challenge myself, but this shirt has passed the test of time., however, I no longer can fit inside a medium shirt properly I’m not sure if you can see it in the picture, but there is some fading around the collar area