Which revolutionary sustainable packaging innovation was first introduced by Penguin Random House in 2021 for their hardcover bestsellers?

The publishing industry has been undergoing significant changes to reduce its environmental impact. Major publishers and independent bookstores alike have been implementing various sustainability initiatives to address concerns about paper sourcing, production methods, and carbon footprints. This trivia question focuses on one of the most innovative sustainability breakthroughs in recent literary production.

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Algae-based book jackets that decompose into plant food
Mushroom mycelium book covers that can be planted to grow mushrooms
Recycled ocean plastic book jackets with embedded seeds
Carbon-negative dust covers made from atmospheric carbon capture