At 420 denier, they're not really "breathable", but they are pretty durable and in addition to being good brush busters, you could probably pick blackberries all day in them or even deflect land mines...
I bought Frogg Toggs waist highs about 6 years or so ago for my wife. She wore them maybe 20 hours? I take great care of my equipment, I expect them to last. So I wore them several times last year, as I recall around 40 hours max. And they fell apart. Never again will I buy anything from Frogg Toggs. Really like my Chota Hippies.