If you look for excellent fountain pen paper, you have to try the Japanese brand Graphilo. Graphilo paper is explicitly developed with and for fountain pen users. Ink lines are accurate, and the back of the Graphilo paper also meets all writing qualities. Graphilo has a special coating that allows high shading and sheen without bleeding and hardly any ghosting. Consequently, it has a long drying time.
Loose sheets of Graphilo paper are available in A4 and A5. One pack contains 50 sheets.
Graphilo is a classy and excellent paper for fountain pen users and anyone who likes beautiful stationery. It's not cheap but well worth the price.