Your books already know what you want to read next.

A used book is a book that doesn't need printing.

Printing one copy of about 300 pages emits around 1.2 kg of CO₂ across raw materials, plates, printing and delivery. One that's already printed emits nothing: it just changes shelves.

That's why Pecia only looks at the second-hand market. It isn't a stance: it's the only place where the price moves and nothing gets cut down.

Figure from the Spanish Pulp, Paper and Board Association, via Podiprint. It ranges from 250 g to 1 kg depending on paper and inks.