ins . ▁Poly pro py l ene ▁is ▁defined ▁by ▁the ▁rec y cl able ▁pl astic ▁number ▁ 5 . ▁Although ▁relatively ▁in ert , ▁it ▁is ▁vulner able ▁to ▁ult rav io let ▁radiation ▁and ▁can ▁deg rade ▁consider ably ▁in ▁direct ▁sun light . ▁Poly pro py l ene ▁is ▁not ▁as ▁impact - res istant ▁as ▁the ▁poly eth y len es ▁( HD PE , ▁L D PE ). ▁It ▁is ▁also ▁somewhat ▁per me able ▁to ▁highly ▁vol atile ▁g ases ▁and ▁liqu ids . ▁ ▁Pol yst y rene ▁Pol yst y rene ▁is ▁manufact ured ▁in ▁various ▁forms ▁that ▁have ▁different ▁applications . ▁Ext r ud ed ▁pol yst y rene ▁( PS ) ▁is ▁used ▁in ▁the ▁manufact ure ▁of ▁dispos able ▁cut l ery , ▁CD ▁and ▁DVD ▁cases , ▁pl astic ▁models ▁of ▁cars ▁and ▁boats , ▁and ▁smoke ▁det ector ▁hous ings . ▁Exp and ed ▁pol yst y rene ▁fo am ▁( E PS ) ▁is ▁used ▁in ▁making ▁ins ulation ▁and ▁pack aging ▁materials , ▁such ▁as ▁the ▁" pe an uts " ▁and ▁m old ed ▁fo am ▁used ▁to ▁c ush ion ▁frag ile ▁products . ▁Pol yst y rene ▁cop ol ym ers ▁are ▁used ▁in ▁the ▁manufact ure ▁of ▁to ys ▁and ▁product ▁cas ings . ▁ ▁Poly vin yl ▁ch lor ide ▁Poly vin yl ▁ch lor ide ▁( P VC ) ▁is ▁a ▁t ough , ▁light weight ▁material ▁that ▁is ▁dur able