This is an Epsilon Series sketchbook by Stillman & Birn. The paper weight in the Epsilon Series is 100 Lb./150 GSM and it has a Natural White Plate Surface. Bright white, it's intended for all pen and ink work, without feathering. It is available in both hardbound and wirebound formats.
Stillman & Birn is a line of premium sketchbooks based on a simple premise: When it comes to sketchbooks, paper matters. You will feel the quality of these high performance papers as soon as you open a book. Furthermore, the Stillman & Birn program offers a unique choice of paper weights, shades and surfaces, which allow the artist to use a wide range of dry and wet media.