After experimenting with many different weights of paper for endpapers, an experienced binder from the Dunedin Public Library recommended 150gsm offset, which we have found to be very suitable. We're offering 160gsm offset paper here as a cost effective alternative. The paper is supplied at 450 x 640mm, 50 sheets to a pack.
We generally use this for making the endpapers for hardcover books of any size. It's best if you fold the endpaper with the grain of the paper, which in this size runs the length of the sheet.
The paper can be easily cut with a craft knife and a straight edge, such as our 500mm stainless steel ruler.