Almost 1.2 billion long-lasting insecticidal nets (LLINs) have been procured for malaria control. Institutional buyers often assume that World Health Organization (WHO) prequalified LLINs are functionally identical with a three-year lifespan. We measured the lifespans of three LLIN products, and calculated their cost-per-year of functional life, through a randomised double-blinded prospective evaluation among 3,420 study households in Tanzania using WHO-recommended methods. Primary outcome was LLIN functional survival (LLINs present in serviceable condition). Secondary outcomes were 1) bioefficacy and chemical content (residual insecticidal activity) and 2) protective efficacy for volunteers sleeping under LLINs (bite reduction and mosquitoes killed). LLIN median functional survival was significantly different: 2.0 years for Olyset, 2.5 years for PermaNet and 2.6 years for NetProtect. Functional survival was affected by accumulation of holes resulting in users discarding nets. Protective efficacy also significantly differed between products as they aged. The longer-lived nets were 20% cheaper than the shorter-lived product.