Di2 Electric Wire Cover for EW-SD300
The Shimano Di2 wire cover sheath is a set of self-adhesive wire covers. They allow you to easily and cleanly route electric wires outside your frame. It also protects E-TUBE wires from wear and tear. These covers are available in black and white and at the time of writing the only available length is 300mm.
Make sure your frame is real clean, peel off the tape on the back, route the Di2 electric wire through it and stick it on your frame. They don't always stick that well, but when they do they'll stay on forever.