In general, running headphones need to be waterproof to weather the conditions of a workout. Headphones contain small and sensitive electronics that can be damaged by moisture from rain or sweat, so any pair of running headphones worth considering will have an IP rating of at least IPX3, like our most comfortable pick, the Ultimate Ears FITS. If you work out in particularly muddy or salty environments, the super-rugged IP68-rated JBL Endurance Peak 3 are probably the best option.