Roofing felt.

There are many different types and grades of roofing felt. Basic BS747 Type

1E fibre based felt is poor - maybe 10 years life expectancy max. Type 3E with glass base is better, probably 15 years max. At the other end of the scale, High Performance Polyester based felts are MUCH better (but expensive), some manufacturers will guarantee the best grade (HT350) for up to 60 years. All this assumes good workmanship and laying in favourable conditions, which are usually the cause of premature failure.