I just got these strings today. They are pretty interesting so far. They are about the same thickness as the Eurosonic Ultra Lights that I was using. The G is a bit thicker and the other strings are a bit thinner I think than the Eurosonics. They sound very much like gut. The G and D especially. All 4 strings are a very even tension. The E and A are steel and the G and D I belive are aluminum wrapped on a synthetic material, but they sound good together-very even. They were $190. So that is a lot of money, but I think alot of bassists here especially those who like like gut might like these. I am going to give them a week or so and see how they settle in. Right now they are a little too boomy for what I like. They have a big fundamental, but I like some growl and a singing sound, so I will see how they turn out. As far as arco goes, these are the best arco strings I have ever used. For sure. They have kind of a gut sound, but very smooth and very easy to play. You can only get these strings by calling H. E. Woolsey at Boaz Music in L.A. (310-559-1213) You can't order them of his website, and I don't know if he uses email. He is an older man, who designed and made these strings himself.