Ntev npaum li cas cov tsho tiv thaiv mos txwv nyob ntev?

Mos armor: 5-7 xyoo (UV raug thiab hws degrade fibers).

Cov phaj tawv: 10+ xyoo (tshwj tsis yog tawg lossis puas).

Nco ntsoov xyuas cov chaw tsim khoom cov txheej txheem kom tas sij hawm.