Hmm, I have the mid zeros and sub zeros; never heard of the Firewall tights. I can wear the sub zeros in the 30s, however, I also tend to wear my Ibex tights that I wear x country skiing. I also do not regularly ride when it's in the 20's, although that's not to say the mercury has not ever slipped below 30 when I've been riding. The Ibex have a wool back and are more windproof. The Firewall tights kind of sound like a pair of tights my DH has. Total windproof, sort of heavy, almost neoprene material. He rode to work one morning last winter, in them, when it was 18 degrees.