That's a great question! Our A5 Leather Journal is made with 100 pages of beautiful, eco-friendly recycled cotton rag paper. It's lovingly handcrafted and designed to be a joy to write on. According to a recent customer, their biro ink works wonderfully and it's a pleasure to write on. While we haven't specifically tested every single pen type, the cotton paper is generally quite thick and absorbent, making bleed-through much less common than with standard paper. It's perfect for journaling, sketching, or taking notes.