) ▁are ▁commonly ▁used ▁as ▁exterior ▁doors ▁because ▁they ▁provide ▁more ▁ins ulation ▁and ▁strength . ▁ ▁Sk in ▁– ▁The ▁front ▁and ▁back ▁faces ▁of ▁the ▁door ▁are ▁then ▁covered ▁with ▁wood ▁v ene er , ▁thin ▁p lywood , ▁sheet ▁metal , ▁fi berg lass , ▁or ▁vin yl . ▁The ▁wooden ▁materials ▁are ▁usually ▁layer ed ▁with ▁the ▁gra in ▁altern ating ▁direction ▁between ▁layers ▁to ▁prevent ▁war ping . ▁F i berg lass ▁and ▁metal - fac ed ▁doors ▁are ▁sometimes ▁given ▁a ▁layer ▁of ▁cell ul ose ▁so ▁that ▁they ▁may ▁be ▁st ained ▁to ▁look ▁like ▁wood . ▁ ▁M ould ed ▁doors ▁▁ ▁St iles ▁and ▁rails ▁– ▁As ▁above , ▁but ▁usually ▁smaller . ▁They ▁form ▁the ▁outside ▁edges ▁of ▁the ▁door . ▁ ▁Core ▁material : ▁Material ▁within ▁the ▁door ▁used ▁simply ▁to ▁fill ▁space , ▁provide ▁rig id ity ▁and ▁reduce ▁drum iness . ▁ ▁H ollow - core ▁– ▁O ften ▁consists ▁of ▁a ▁lattice ▁or ▁h oney comb ▁made ▁of ▁cor rug ated ▁card board , ▁extr ud ed ▁pol yst y rene ▁fo am , ▁or ▁thin ▁wooden ▁sl ats . ▁Can ▁also ▁be ▁built ▁with ▁st agger ed ▁wooden ▁blocks . ▁H ollow - core ▁m old ed ▁doors ▁are ▁commonly ▁used ▁as ▁interior ▁doors . ▁ ▁Lock ▁block ▁– ▁A ▁solid ▁block ▁of ▁wood ▁mounted ▁within ▁a ▁h ollow - core ▁flush ▁door ▁near ▁the ▁b olt ▁to ▁provide ▁a ▁solid ▁and ▁stable ▁location ▁for ▁mount ing ▁the