Aquila, the Italian string company, have released their ‘Red Series’ strings, a new type of ‘Nylgut’ mixed with a copper compound to increase the density of the string. This makes the lower notes, like the ‘Low G’ on a Tenor attainable without using a wound string. This, in turn, avoids the scratching sound as your fingers slide up and down the fretboard, as well as equalising the sometimes overly bright sound of a wound string compared to the rest of the Nylgut strings.
The new Red strings feel a little more flexible, some might say rubbery, than the original white Nylgut out of the packet, but once strung up the difference in feel is virtually nil, except for perhaps a very slight rough or gritty texture compared to the whites.
There does seem to be a good deal of stretch in these red versions, as can be seen from the amount wound onto the tuner after fitting them hand tight prior to wind-on.
They do, however, sound nice and certainly eliminate the noise of fingers sliding over them.