I think Oregon is one, not sure but there are a couple of others. The best thing is to thoroughly clean and sanitize them in bleach solution. I fished the SH last spring and didymo was everywhere. I soaked my boots in the solution in the tub for about 36 hours, rinsed with hot water, and dried them outside in the sun, turning them to catch the maximum sun.
Fly Fish America did a test on felt and synthetic rubber. Anglers were given one boot with one and another boot with the other. If I recall the felt was given the edge on traction. FWIW, my wife started trout fishing with a pair of Easy Spirit sneakers. Surprisingly, she got good traction in the Smokies.