I posted an article on Protecting your collection on

http://www.andre-norton.org/

It includes the address & phone numbers (computer addresses) of a few dealers who specialize in Book protection.
These include Brodart - who will charge about $5 for 25 covers of any one size.

I suggest purchasing 3 sizes, in a style that you prefer. I usually pay the extra few cents for the 'long' lengths, and order sizes of 8, 9 and 10 inches high. The style that I prefer is clear on the front & has a center slit in the backing paper. This makes it easy to fold down the clear part to exactly fit the book. I never have to fold down more than .75 inch.

The old books take an 8 inch cover, and many new books need about 9.5 inches.

I usually replace the dust jacket protector on the X-library copies in my collection. I usually find that the jacket protectors have become dirty, through use, and the nice new jacket feels better.
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Aethlings's Norton site