Carbon fibre flap to go under the rear mudguard , stops all the muck getting into the airbox and gives the rear mudguard more support.
Made by Mitani Japan and just works! Yes they are expensive, but they do work.
Longer and better and completely different from the Honda one!
2014 - 2019- All models. (will fit 2009 on but this sits better on new shaped 2014 onwards mudguard)
 
A customer review - "I reckon riders accept that crap just gets in. Well it doesn’t with this. OEM is 40 odd quid and trick bits is junk... doesn’t take much thinking about!"
 
"Adopting a tension attachment method so that there is no gap between the R fender and the stabilizer, the shape is closely attached to the fender! 
The strongest way to prevent the infiltration of air BOX with mud and water! Factory rider item!
It is possible to sit on the R fender and to grip the R tire while sitting in a muddy running or stacking by rear weighting on slippery roads! If there is no stabilizer, the R fender will bend and no weight will be applied."