Its for 100 amp service . Is pvc to code ? Or should I use something else ? The wire needs to be run outside my home and back in so I don't have to open the ceiling up .

Not sure what you are doing. Are you adding a sub-panel?

Set I am adding a sub panel . There is a small sub panel in the closet in the bathroom but it is under powered. I need to bring more power into it because I am putting in a kitchen . It is easier to run the wire out the house and back in ?

Rather than run the wire through the beams and open up the ceiling . I just want to know ehrn I get outside what is the appropriate tubing to use when the wire is out side? Pvc? Steel? Etc?

PVC is fine, however, if PVC is run horizontally, it will sag, even if you strap it every three feet, so I recommend metal raceway, simplest being EMT with raintight compression connectors and couplings.

With conduit, you would use copper wire with THWN insulation or aluminum wire with XHHW insulation, individual conductors, for example, 3 #2 AL XHHW plus a #6 AL XHHW for the equipment ground.

To begin with here in Virginia, if you are going to add a circuit to the main service panel, you must have a permit to do the work. So I ask you, what does your local authority having jurisdiction have to say on this matter?

"There is a small sub panel in the closet in the bathroom but it is under powered."

Circuit breakers/fuses of any kind are not allowed in bathrooms or closets, by current code standards.

Second, what do you mean by "Under powered"?

A sub panel is required to have one four wire feed to it, which is why TK's example gives you a four wire setup.

What is the listed size of the panel you already have installed? If the panel is listed for 40 amps, you cannot run 60 amps to the panel. Nor can you run a new circuit to the panel to bring more power to the panel. There can be only one feeder for the panel.

Can you be a bit more descriptive about what you are trying to do, please?

P.S. What do you mean that you want to supply power from the sub panel to your kitchen? How much amperage are you planning to bring to the sub panel?