NEW YORK, Dec. 31 (UPI) -- While traditional pop-up books are oriented towards children, a new breed aimed at a more adult audience is starting to flood U.S. bookstores.

The New York Post said that with such new literary works such as "The Pop-up Book of Sex" and "The Pop-up Book of Celebrity Meltdowns," the former children's genre is now being embraced by adults.

While "Sex" may take on a very adult topic, its paper engineer Kees Moerbeek ensured potential readers that the adult work does have its limits.

"The restriction was not to show any visible penetration," Moerbeek explained. "But it's so much more effective to give suggestions of sexual activity than revealing the actual act."

Pop-up author Robert Sabuda said that such new suggestive works are representative of a new trend in the genre away from traditional children's literature.

"There are more pop-up books for adults than ever before," Sabuda told the Post. "And the pushing of the envelope of what the material can be is American attitude, just going as far as it can go."