On the Arabic and Turkish oud sets, the 3rd strings (D and E note) are normally wound (as well as the 4th D on the Iraqi oud set). A wound string has a bright sound but, at the same time, it is fragile, expensive and gets rusty in a short time.
Aquila Corde has introduced a new invention: the 3rd unwound strings. These strings are made using a special bio-plastic loaded with metal powder in order to increase the density. The performances are far better than a traditional wound string.
The new unwound strings last for a long time, they are very stable, and they have a perfectly smooth polished surface.