Number One – Temperature and Relative Humidity
Heat speeds up chemical reactions and thus paper decomposition. Lower temperatures are actually very good for paper, but not for humans to live in, so a low temperature is not really practical advice here. High humidity means there is a lot of moisture in the air, and when there is a lot of moisture in the air, mold and mildew can form on paper. Low humidity, on the other hand, can cause paper to dry out too much and become brittle. In an environment where relative humidity fluctuates, paper expands and contracts with moisture gains and losses, and it experiences structural stress, becoming unstable and easily susceptible to damage. Therefore, fluctuations in both temperature and relative humidity should be avoided. Lower temperatures and stable (ideally 35-45%) relative humidity are best for books.
- Do not place your books on an outside wall that will be cold in the winter and warm in the summer.
- Do not place your collection near heating or cooling vents so hot or cold air blows directly on them.
- Make sure your books are not jammed in too tightly together on a shelf. Good circulation helps prevent pockets of still air, which allow for mold to grow more easily.