50 - 65 degrees Fahrenheit. Consistency is also critical. 50 degrees one day and 65 the next is not good and will cause accelerated aging.
Bear in mind that very cold temperatures are can cause damage and drying of the paper (freeze drying).
Ideal Relative Humidity
50% RH +/- 10% is generally best. Like temperature, avoid storing in areas where there are quick and wide fluctuations in RH.
Bear in mind that extremely low RH can dry paper out. You can have white pages that are brittle!
Books should be stored in a dark environment. Incandescent lighting should be used and windows should have blinds to minimize direct sunlight.
Fluorescent bulbs emit stronger UV rays and will degrade comics faster than regular incandescent lighting.
Fluorescent bulbs can damage paintings and textiles which have light-sensitive dyes and pigments. Strong colors will tend to fade on exposure to UV light. Ultraviolet light can also cause polymer degradation with a loss in mechanical strength and yellowing of colorless products.
Storing Slabbed Comics
Can CGC slabs be vacuum sealed?
"No. Our inner well is designed to allow the book to breathe as it is not hermetically sealed, which would probably quadruple our cost if we did so. It is not safe for a book to be air tight if it is not hermetically sealed."
How do I stored a CGC slab?
"We suggest that all graded comics be stored as you would any other comic, standing upright in an archival safe comic box in a cool dry place."
CGC responses from Wm. Eric Downton, CGC Receiving Manager
NOTE: Some collectors have suggested that vertical storage exerts downward pressure on the staples over time. So, it has been suggested that if the slab is stored flat, it relieves any stress on the spine and staples. Currently, there is no evidence that there is any potential harm in this method. Please bear in mind that flat storage is not suggested for unslabbed comics as it may cause spineroll. With the hard outershell and uniform depth, spineroll is not an issue with slabbed books.
Tips / Hints
* Books from attics are tanned and brittle. Books from basements are musty with rusty staples.
* What's above your books? Do not store books in an area below water lines that could spring a leak or bathrooms/laundry rooms that could flood.
* If your basement is an acceptable storage environment, be sure books are at least a foot off the floor.
* Never set your boxes directly on concrete. Concrete conducts cold and wicks moisture.
* Use a fan to circulate air if the room is large and/or full. This ensures even temperature and RH throughout the room and prevents the creation of "micro environments" in cramped spaces.