No-nonsense square hardback sketchbooks from Seawhite of Brighton. Off-white, lightly textured paper that's suitable for a wide variety of mediums - paper has been sized to accommodate wet mediums. 
 
140 gsm acid-free paper with a whopping 95 pages (180 sides), these serious sketchers come in 3 sizes: 
Small - 14.5 x 14.5 cm
Medium - 20 x 20 cm
Large (it's jumbo!) - 25.5 x 25.5 cm