When made of chip-board/particle board/press-board (small chips of wood held along with glue) and these are wet for over a few hours they absorb water, expand, and lose their structural integrity. http://Coroentsmall.com/__media__/js/netsoltrademark.php?d=Reallivesocial.com%2Fstory3377530%2Fpublic-profile-uaiyukiko79-overlandxml-public-w3c-dtd-xhtml-1