Cov kav dej yuav khov. Tsuav yog qhov ntsuas kub hauv cheeb tsam tsis txaus thiab tsis muaj kev tiv thaiv kev tiv thaiv khov, cov dej hauv cov kav dej yuav khov. Dej yuav nthuav dav thaum nws khov, thiab cov kav hlau zoo ib yam, xws li cov kav dej galvanized, feem ntau khov thiab tawg vim qhov tsis zoo lub zog ntawm qhov kub thiab txias, ua rau muaj xwm txheej.
PPR dej yeeb nkab yog ib feem yas, uas muaj peev xwm hloov cua sov tsis zoo thiab muaj peev xwm tiv thaiv kom khov. Piv nrog cov kav hlau, nws tsis yooj yim rau khov, thiab vim nws tus kheej lub zog tensile, nws tsis yooj yim kom khov thiab tawg hauv qab qhov txias.