Do Shimano STIs take special cables / housings? I am building my first bike with them. I have some Tiagra 9sp shifters i am going to use.

I have read that Jagwire will work but some say they dont work well. DO i need a special shimano cable kit for good performance or is that just marketing to get you to spend more money on shimano? IT seems the PFTE cables are the ones you want. Perhaps this is a shimano technology?

I use Shimano and Jagwire interchangeably; I use the lined housings and the die-drawn stainless inner wires. As the coefficient of friction of steel vs PTFE is almost the same as PTFE vs PTFE I see no advantage to coated inner wires.

There is no need for you to buy the Shimano brand shifter cables. There are many brands that sell cables at a variety of price points. More expensive cables will maintain high quality shifting for longer, and are less easily damaged by water and grime.

Brake cables and shifter cables are NOT the same thing and are not interchangeable.

Just make sure you get non compressible (indexed) shift housing to get the best shifting performance.

Jagwire works great - worth the extra price if you want one of their cool color schemes, otherwise whatever the bike shop sells is fine.