This method is a solution for materials that have suffered extensive water damage. This process calls for very sophisticated equipment and is especially suitable for large numbers of very wet books and records as well as for coated paper. Books and records are placed in a vacuum chamber frozen. The physical process known as sublimation takes place - i.e., ice crystals vaporize without melting. This means that there is no additional swelling or distortion beyond that incurred before the materials were placed in the chamber.
Many coated papers can be difficult to dry without sticking together once they are wet.
They may then be vacuum freeze dried with a high potential for success. Rare and unique materials can be dried successfully by vacuum freeze drying, but leathers and vellums may not survive. Photographs should not be dried this way unless no other possibility exists. Consult a photograph conservator. If only a few books are dried, vacuum freeze drying can indeed be expensive.