Oh... pitched roof felt. :lol:
There are 3 main options for underslating/under tile felt:
1. A breather membrane - i.e. Dupont Tyvek, Klober Permo, Monarflex 700 - lets the your roof breathe, strong but expensive £80-£120 for a 75m2 roll.
2. A non breather - Dupont Eas1felt, Klober...