Check to see if the warped pages are brittle since exposure to sunlight often makes the paper brittle and easily-crumbled. If they are brittle, you will have to soften them.
Wet a piece of cloth in water and gently moisten the warped pages to make them soft. Place a sheet of wax paper between every warped page to prevent it from becoming glued to the next page.
Close the book tight and place three to five books, or weight of about 5 lbs. on top to straighten the warped pages.
Flatten the warped pages with care and shut the book tight without moistening. Use this procedure straightaway if the pages are not brittle. Put the book on a flat surface, such as a table or the floor, and pile three to five heavy books from your library on top of it. Leave it for one to three days and check to see if the warped pages are now smooth.
Iron the pages at the lowest temperature setting to flatten the warped pages.
Protect books from direct sunlight. Store them in a cool room with temperature below 68 degrees F and a relative humidity of 50 to 60 percent.