When Shimano developed the 9000 series Dura-Ace a new cable and housing system was engineered to truly augment the lever and component function, and reduce friction and drag to enhance feel and subtle performance without extraneous effort. This system carried over to the R9100 generation. The cables earned a new polymer coating and the brake housing was specifically developed for the lever and caliper interaction. The Dura-Ace BC-9000 Brake Housing is more flexible, with less drag, and it's liner is coated with a special synthetic grease (not the SP41 silicone) to be used with the 1.6mm Polymer Brake Cable. Sold here in a 40 meter roll in a shop-use file box, dedicated Dura-Ace R9100 and 9000 users can service their bikes at home with the proper BC-9000 housing, and save money by buying in bulk. You also generate less waste, cutting to exact length, which increases savings over housing kits.

Sure, you need to change your cables and housing numerous times on multiple bikes to go through a 40 meter roll, but racing cyclists and high mileage riders generally change their cables and housing regularly, and when you want to do the work yourself, it helps to have the right products on hand. In the case of the low-effort, well modulated braking of the Dura-Ace dual control levers and SLR-EV brake calipers, you lose performance by using an alternative housing. Any cyclist who has invested in Dura-Ace performance and overall experience knows why using the specified product matters, and in the case of the BC-9000 Brake Housing there truly is no replacement.