The tubing that I use to protect from cable slap is "Jagwire Black Housing Liner", part no. CA2206. When I used donuts, they ended up migrating and becoming ineffective. The housing liner just works.

The liner is for cables up to 1.8mm, comes in a 30meter roll, and the package describes it as teflon.

About $8.00 for a roll, and 30m should do a lot of bikes.

http://www.jensonusa.com/store/produ...ing+Liner.aspx