Fit/Comfort
The concept behind this 7-liter pack was to lighten up (by a whopping 50 percent!) Nathan’s popular VaporCloud and Vaporshadow packs while preserving Nathan athletes ability to carry all their mandatory gear at the Ultra-Trail du Mont-Blanc. True to its name, the VaporAiress feels exceptionally light. It rides comfortably high on the back, with adjustable sternum straps and over-the-shoulder “load lifters” to dial in the fit. With both the men’s VaporAir and women’s VaporAiress packs available in three sizes each, Nathan has done a commendable job stepping away from the one-size-fits-all model and working to accommodate a wide variety of body types. Do note that it fits a bit large, so if in doubt, size down.

Carrying Capacity
This was the biggest disappointment of this pack. Although it advertises 7 liters of storage capacity, I found it difficult to stash anything substantial in this pack as compared to other packs in this test. The narrow, non-expandable fabric of the compartment made it difficult to accommodate awkward or bulky items like a brimmed running cap or large headlamp. The main rear compartment held only a few items before its capacity was maxed out, and the external bungee was not substantial enough to hold much of anything. With just a couple cords (rather than a full criss-crossing bungee web), most items I tried to stash in the external bungee wound up falling out after a few minutes of running and jostling. The side mesh pockets are great, though they require a great deal of elbow mobility to reach while wearing the pack. 

Function
There are lots of nice ideas at work here, including a whistle and ample front pockets for easy, on-the-go access to essentials like snacks and electrolyte pills. As with the Ultimate Direction PB Adventure Vest, though, I don’t love the side-zipper entry into the main compartment, as I find it easy for items to accidentally fall out of it while accessing my gear. Likewise, gels and gel-wrapper trash fell out relatively easily from the loose, non-bungeed pockets on the outside of the front bottle pockets.

Hydration System
The included 70-oz reservoir on this pack is excellent. As a top-loading reservoir, it’s easy to press excess air out of it to minimize liquid sloshing on the run. The easy on/off bite valve stays in put with a magnetic clip along the sternum strap—a handy innovation that I certainly appreciated. It was difficult to re-insert a full hydration reservoir into a fully loaded pack; a lot of the gear had to be removed from the pack in order to get the reservoir back in—far from ideal for race scenarios.

Two front-bottle pockets also exist, though bottles are not included. 

Versatility
This could be a great pack for daily training runs or relatively well-supported races, but I found it too small to fit everything I need for long solo adventures in the backcountry, or to accommodate the full mandatory kit for the Ultra-Trail du Mont-Blanc for which it was purportedly designed.I do appreciate the option to use either the included hydration reservoir and/or the front-bottle pockets. I also grew excited when I saw the trekking-pole loops on the rear, as they offer fully adjustable cinches to keep the poles in place while running. (Many other comparable packs offer non-adjustable, elastic loops, and with enough jostling, poles tend to slip through these.) However, the loops are placed awkwardly on this high-riding pack, so that I felt my trekking poles digging into my shoulder blades as I run; unfortunately, this rendered them un-usable to me.

One final complaint on the VaporAiress: while the men’s VaporAir is available in two different, tasteful color ways, the women’s pack is available only in hot pink with orange trim. On a personal level, I would appreciate a second, subtler color option, just as the men have.