Where did montag hide his books after the ladies left his house?

Montag was hiding books in 2 instances from his wife. The first instance was near the beginning after they burned the woman. He hid the books in the air vents. The second time was when Beatty came over to talk. He hid it in his pillow and Mildred wanted to fluff the pillow.

References:

Ray Bradbury, Fahrenheit 451, New York: Ballantine Books, 1953