Aquila 107U strings set for tenor ukulele. Mix of Red and Super Nylgut. The innovative Red Series adds red copper powder to Nylgut to nearly double the density, allowing players to tune in Low G but keep the same sound power, quality, and intonation. The Red Series feels slightly rough, a texture that eliminates the slight squeak sometimes heard with Nylgut. Considered an upgrade to New Nylgut, Super Nylgut strings have a smooth, polished surface that feels like wax. Super Nylgut is not as stretchy as New Nylgut, which allows for quicker setting to the proper intonation when new and stronger intonation maintenance. Super Nylgut is more resistant to sharp nut edges, fret markers, or hard nail playing.