is the IN2 epoxy infusion resin UV stable or do parts need any extra protection from a UV clear coat?

No such thing as a UV stable epoxy, that's just their nature. Some have stabilisers added to increase resistance, but it's a question of time. All epoxies will degrade with UV exposure unless they are protected. 

OK Thanks, so infused parts that will be outside need to be clear coated. or use an in mould coating?

IN2 is highly UV resistant for an epoxy but as Hanaldo says. no epoxy is UV proof.

If you need additional protection is down to your environment.  Here in the UK, we have customers and our own parts made with epoxy by infusion that are years old and show no visible yellowing.  You have to remember that the surface resin layer on infused parts is very thin and the bold black colour of carbon means you could have extensive UV yellowing but it is invisible to the naked eye.

For some in sunnier climates or cars outside more may wish more protection, in which case the simplest method is an automotive 2 pack lacquer professionally sprayed onto the part. Almost all professional automotive lacquers are UV stable to protect the base coat colours on modern 2 layer paint systems.

Alternatively you can use a UV stable gelcoat in the mould such as our GC50.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant