PFAS are only used on outside (shell) layers in outdoor gear. It would do nothing on a wool t-shirt like that, you need a solid nylon barrier shell, which is th

PFAS are only used on outside (shell) layers in outdoor gear. It would do nothing on a wool t-shirt like that, you need a solid nylon barrier shell, which is then coated to make the surface hydrophobic so the water beads off. Most consumer merino wool nowadays contains nylon because it makes it more durable- ultra soft merino wears out and develops holes rapidly without adding a small amount of nylon “scaffolding” which adds strength and chafe resistance. When merino socks first hit the market, for example, they would sometimes only last a few days of hiking… nowadays a nylon wool blend sock will last years and years of hard use. These layers are not designed to be waterproof or hydrophobic- the opposite actually, they are designed to absorb moisture so they are “moisture wicking” keeping the skin dry.