▁If ▁it ▁is ▁three ▁p ly , ▁the ▁third ▁p ly ▁is ▁often ▁p lywood ▁that ▁runs ▁parallel ▁to ▁the ▁l am ella . ▁St ability ▁is ▁gained ▁through ▁the ▁gra ins ▁running ▁per pend icular ▁to ▁each ▁other , ▁and ▁the ▁expansion ▁and ▁contra ction ▁of ▁wood ▁is ▁reduced ▁and ▁re leg ated ▁to ▁the ▁middle ▁p ly , ▁stopping ▁the ▁floor ▁from ▁g apping ▁or ▁cu pping . ▁F ib re board : ▁The ▁core ▁is ▁made ▁up ▁of ▁medium ▁or ▁high ▁density ▁fib re board . ▁Flo ors ▁with ▁a ▁fib re board ▁core ▁are ▁h yg ro scop ic ▁and ▁must ▁never ▁be ▁exposed ▁to ▁large ▁amounts ▁of ▁water ▁or ▁very ▁high ▁hum id ity ▁- ▁the ▁expansion ▁caused ▁from ▁absor bing ▁water ▁combined ▁with ▁the ▁density ▁of ▁the ▁fib re board , ▁will ▁cause ▁it ▁to ▁lose ▁its ▁form . ▁F ib re board ▁is ▁less ▁expensive ▁than ▁tim ber ▁and ▁can ▁emit ▁higher ▁levels ▁of ▁harm ful ▁g ases ▁due ▁to ▁its ▁relatively ▁high ▁ad hes ive ▁content . ▁An ▁engine ered ▁flo oring ▁construction ▁which ▁is ▁popular ▁in ▁parts ▁of ▁Europe ▁is ▁the ▁hard wood ▁l am ella , ▁soft wood ▁core ▁laid ▁per pend icular ▁to ▁the ▁l am ella , ▁and ▁a ▁final ▁backing ▁layer ▁of ▁the ▁same ▁noble ▁wood ▁used ▁for ▁the ▁l am ella . ▁Other ▁noble ▁hard wood s ▁are ▁sometimes ▁used ▁for ▁the ▁back ▁layer ▁but ▁must ▁be ▁compatible . ▁This ▁is ▁thought ▁by ▁many ▁to ▁be ▁the ▁most ▁stable