These are nylon core strings and although another European maker makes them too, there is no comparison. For use strictly with piezo based pickups, these have a lovely rubbery feel and sound. Very low tension which for many players is a bit difficult to deal with initially. if the more organic DB type sound is what you want then there is nothing like these. I've been using them for years but find some of Thomastiks products can be a little variable in quality. I accept that one pack in every five or so is not up to standard and even though they are costly, as above, there is nothing to rival them. Because of the construction, a lot of the metal to metal/string noise to fret/piezo quack is reduced without having to turn the treble right down. On a fretless, they are great. Truss rods will need to be backed off when using these after steel core strings.