This synthetic paper has made the best endpapers we've ever used. It's tough, durable, and resistant to buckling.
The paper is supplied at 450 x 640mm, 50 or 10 sheets to a pack, or at 450 x 320mm 50 or 10 sheets to a pack.
We generally use this for making the endpapers for hardcover books of any size. The direction of the grain is not crucial with synthetic paper, so you can fold either way for good results.
The paper can be easily cut with a craft knife and a straight edge, such as our 500mm stainless steel ruler.