Are particle-board bookshelves strong enough to hold a full library?

Across the reviewers we read, the consensus is that laminated particle-board shelves (Sauder, ClosetMaid, Furinno, IKEA Billy) hold standard book loads fine when assembled correctly and anchored to a wall, but they sag under dense hardcover collections over long spans. Threads on r/HomeLibraries and r/BuyItForLife repeatedly recommend solid wood or shorter shelf spans for heavy book loads, and verified-purchase reviewers note that the back panel is a critical structural part — skipping or misaligning it is the most common cause of wobble.