My old bike, which used to have Di2, has internal cable routing. I'm now re-building it up with cables (the Di2 bits having been cannibalised for my new bike).
When doing my pre-project shopping I got some white cable liner - ie the thin stuff, not strong like cable housing. But do I need it, is it advisable / optional...?
If I do need it, how much do I use - as much as possible, right through to the mech - or just a little bit where the cable goes under the bottom bracket?
Or does it depend on the inside of the specfic frame?
ISTR recall when I bought the frame 8 years ago that it may have had some of this stuff in it then, but I didn't know what it was and thought it was just a form of plastic string to guide cables through.