"Kevlar is an Aramid fiber. It is stronger than steel per unit weight, which is one of Kevlars inherant advantages over steel. However, Kevlar is very susceptible to degradation secondary to cummulative UV exposure, and will succumb to rapid mechanical weakening caused by flex cycles. For these reasons, Kevlar is not a good long term brake line material for a street or typical track bike application." someone on another forum ask the same q and this is the response. Ive had SS on my old bike and had no problems, id go with either when i buy some for my new bike