The Nathan VaporAir 4.0 8L is a unisex hydration vest for long trail runs and other outings where water, nutrition and spare layers need to remain accessible. It includes a 2-litre Nathan x HydraPak bladder with a quick-release hose, while the two front flask pockets can each hold a soft flask up to 591 ml; front flasks are sold separately.
Nathan specifies an 8-litre storage capacity and a weight of 219 g without the bladder, or 304 g with it. Four expandable front mesh pockets, an internal zipped valuables pocket, two pass-through side pockets, a rear main compartment and an external bungee provide several ways to organise gear. The ripstop body and two-layer mesh are designed for durability, airflow and quicker drying.
Fit can be adjusted while moving through front toggles, an internal wrap panel and sliding sternum straps. The vest is offered in S–M, L–XL and XXL size ranges, so runners should check Nathan’s size guide rather than treating it as one-size-fits-all. Capacity and weight figures are manufacturer specifications, not results from independent testing. The US$160 regular price and specifications were checked on Nathan’s official US product page on 23 October 2026.
