▁autom ob iles ▁since ▁the ▁ 1 9 7 0 s . ▁ ▁Labor ▁costs ▁to ▁build ▁an ▁Alle w eder ▁are ▁significant ▁due ▁to ▁the ▁many ▁riv ets ▁and ▁riv et ▁holes . ▁ ▁Also , ▁the ▁choices ▁of ▁aer od ynamic ▁shapes ▁are ▁limited ▁by ▁the ▁form ability ▁of ▁the ▁al umin um ▁sheet . ▁ ▁That ▁said , ▁al umin um ▁is ▁relatively ▁in exp ensive , ▁and ▁as ▁of ▁ 2 0 1 7 ▁Alle wed ers ▁can ▁be ▁often ▁be ▁bought ▁for ▁less ▁than ▁other ▁designs ; ▁they ▁can ▁also ▁be ▁bought ▁as ▁k its , ▁to ▁reduce ▁out - of - po cket ▁cost . ▁ ▁Al umin um ▁can ▁also ▁be ▁rep a ired ▁relatively ▁easily , ▁and ▁al umin um , ▁which ▁is ▁hom ogeneous , ▁can ▁be ▁rec yc led ▁more ▁easily ▁than ▁many ▁composite ▁materials . ▁ ▁Another ▁common ▁modern ▁design ▁is ▁a ▁mon oco que ▁shell , ▁often ▁made ▁of ▁fi ber - re in for ced ▁pl astic ▁or ▁" FR P ", ▁plus ▁sub - frames ▁of ▁w eld ed ▁al umin um ▁tub es . ▁ ▁FR P ▁can ▁be ▁used ▁to ▁produce ▁a ▁wide ▁range ▁of ▁shapes , ▁and ▁thus ▁can ▁improve ▁aer od ynam ics ▁over ▁approaches ▁such ▁as ▁" bird c age " ▁and ▁al umin um - sheet ▁mon oco que . ▁ ▁FR P ▁can ▁also ▁use ▁fib ers ▁with ▁high ▁strength - to - weight ▁ratio ▁that ▁in ▁vel om ob iles ▁can