“WHY put dust jacket covers on books, it seems unnatural – don’t they have to breathe?”
Short answer is no: “Books aren’t alive, they don’t breathe.”
Long answer is no: “Books don’t breathe, they SUCK.”
Generally books are made of paper and cardboard – and these materials are highly desiccated (go look it up, I’ll wait.) So, from the moment a book is born its main goal is to absorb as many moisture molecules as it can. Specifically from the air at hand, but if a book is kept near water it will take those evaporating molecules too. That’s why books kept in Seattle and in bathrooms go all mildewy, not to mention books in the bathrooms of Seattle. Many of us working with these sponges end up with dry cracked fingers – and god forbid one works in a warehouse of the buggers in cardboard boxes, you may never breathe right again. Think of books like wine, you are always trying to find a consistent and balanced level of heat and moisture. When and where it is hot and humid you find yourself installing a dehumidifier and when it is overly and prolongedly (hey it’s my language i can make up words if i want to) dry you plug in the humidifier. If you find yourself indecisive you can find machines that do both. Boy, don’t I wish I invented THAT!
So to answer the question, you put dust jacket protectors (and THAT’S what they are called. . . they aren’t called ‘Brodarts’ ever.) on to protect the books from dirty fingered customers, transit damage, shelf rubbing, edge wear, dust, moisture, klutzy employees and spraying cats (is that last one just me?)