For the trip to the airport and from it to Paris you need have special tickets.
The system of public transport RATP offers 3 variants to get to the airport:
- Orly: Orlybus and Orlyval
- Roissy (CDG): Roissybus
There are acceptable and fast options to get to the airport and go back to Paris.
Roissybus is the direct bus from Charles de Gaulle Airport to Opera Garnier in Paris.
Travel time: 45-60 minutes.
Orlybus – the bus from Orly Airport to Place Denfert-Rochereau in Paris.
Travel time: near 30 minutes.
Orlyval if the automatic tube connecting Orly Airport and Anthony (RER B station).
Travel time: near 35 minutes Orly/Chatelet using RER B. 45 minutes Orly/Charles de Gaulle using RER B and RER A
* all the information about these types of public transport you can find on the official RATP site