The main objective of this study was to determine the service life of high-density polyethylene lining when exposed to natural degradation in tropical climates using time-dependant properties. The changes in material density, strength, and strain at fracture over the degradation period were determined. Optical micrographs were obtained to track the changes in the material during aging. An exponential decay equation was developed that estimates of the service life of the high-density polyethylene lining. It was concluded that most of the degradation of the material takes place in the first few months of installation and that both the density and mechanical strength of the material increased in the course of degradation, whereas the fracture strain reduced over time. It was concluded that the most important factor that determines the lifespan of the liner is the ability to maintain high strains. POLYM. ENG. SCI., 51: 1198-1205, 2011. (C) 2011 Society of Plastics Engineers