KAS Fuger Air8 V4 Hydration Vest Review: Lightweight Storage That Runs Bigger Than Its 8L Label

Introduction

KAS may not have the profile of the big trail running brands, but every piece of their kit we have tested has shown impressive quality, attention to detail and clever design choices. The Fuger Air8 V4 is the latest version of a hydration vest we first tested around two years ago, and this generation brings a handful of meaningful updates, including the option to attach a dedicated pole quiver.

After a month of testing, we came away impressed with how comfortable, breathable and surprisingly spacious this vest is. Here is the full breakdown.

First Impressions and Key Specs

The Fuger Air8 V4 retails on the KAS website for £123 and comes in at just 198g in a medium, which puts it firmly in the lightweight running vest category. Storage capacity is officially 8 litres, but the practical layout makes it feel closer to a 10L vest, with plenty of accessible pockets making use of every available space.

KAS offers the vest in a unisex fit across six sizes, from extra small up to double XXL, and in eight different colourways. Our test unit arrived in a red, white and black combination. One note on that: white material on a hydration vest tends to end up grubby after long races, but with eight colour options available, there should be something to suit every taste.

Construction and Materials

The bulk of the vest is built from an antibacterial polyene mesh and a highly breathable 3D honeycomb mesh, similar to the fabric used on Salomon’s popular Advanced Skin 12. Reinforcement points at all the stress areas add durability without adding meaningful weight, and high-viz detailing improves visibility for running after dark.

The two included 500ml TPU soft flasks use a clever diagonal bite valve system. The valves rotate a full 360 degrees, making them easier to drink from on the move, and pushing the valve down locks the flask off completely. That makes them leak-free when you transport the vest to a race or stash a spare full flask in the back.

One particularly nice detail is a shiny silicone lining on the inside of the soft flask pockets, which makes it easy to slide the bottles back in after refilling. It works well, although the right-hand pocket is slightly trickier because of an extra stuff pocket on the front.

Storage and Pocket Layout

This is where the Fuger Air8 V4 earns its space. There are 12 pockets in total, thoughtfully distributed across the front and back.

On the front, each shoulder strap gets a small stretchy stuff pocket up top, ideal for salt tablets or electrolyte tabs, with the two large soft flask pockets below. A small emergency whistle sits on the left pocket, and it is noticeably louder than most whistles fitted to running vests, loud enough to genuinely attract attention in a tricky situation.

KAS also works a double bungee system into the soft flask pockets. In addition to the standard cord at the top, a second cord halfway down lets you cinch the flask tight as you drink and its volume drops, stopping the frustrating slide-down-inside-the-pocket problem entirely.

Moving down the front, two good-sized stretchy pockets hold nutrition, bars and gels for easy access on the move. The right pocket includes a removable rubbish bag with a drawstring attached to a plastic clip that doubles as a key loop. On the left, a secure zip pocket under the soft flask comfortably fits an iPhone 15. One caveat: we would prefer not to have a hard phone sitting against the chest under a flask on long runs.

The back offers even more. There is a separate compartment for a 1.5L bladder with a strap and clip system to keep it secure, a high elasticated stuff pocket for a waterproof running jacket that can be grabbed out on the move, and three segregated rear compartments for mandatory race kit such as a spare base layer, bivvy bag, first aid kit and warm hat. The main and lower stretchy pockets both have generous volume, and the lower one includes an internal secure zip pocket.

Fit and Comfort

KAS vests have always fit well, and this one is no exception. Over a month of testing we experienced no rubbing or chafing, and the vest sits high on the back so it feels secure and virtually bounce-free even when fully loaded.

The closure is KAS’s ADF, or all-round dial fit adjustment system, a corded boa-style setup on the front. You clip in the red clip, then the two black clips top and bottom, and a quick turn of the adjustment wheel dials in the fit. The V4 update adds small rubberised crosses that keep the cords from tangling when unclipped. In practice, the system makes micro-adjustments on the run effortless and lets you personalise the fit precisely.

Real-World Performance and Capacity

Despite looking compact, this vest behaves a bit like the TARDIS: it swallows far more kit than its size suggests. Loading it with basic mandatory kit for a summer 100-mile race, everything fitted in easily, and the segregated storage meant every item had a logical home.

Breathability from the honeycomb mesh proved excellent, and the combination of secure fit, rotating bite valves and the locking flask system made drinking on the move simple and mess-free.

Pole Carrying Options

One of the headline updates on the V4 is compatibility with a dedicated pole quiver, sold separately on the KAS website for £20. It attaches easily and, on long mountainous outings, it is our preferred option: poles sit securely on the back, you barely notice carrying them, and they are quick to pull out when needed.

If you would rather not spend the extra, the vest also includes a front mounting bungee pole system and another along the back, so you have several ways to carry poles out of the box.

The One Drawback

Our single gripe involves the plastic toggles on the cords halfway down the soft flask pockets. Their length means the hard plastic toggles tend to catch on the ADF system on the right and the red buckle on the left, producing an irritating ticking sound while running. It is easily worked around by tucking the cords away or wrapping the toggles in a bit of soft tape, but a softer toggle material would be a welcome change in a future version.

Buying Advice

The KAS Fuger Air8 V4 suits first-time hydration vest buyers and experienced runners upgrading alike. At £123 with two 500ml soft flasks included, it offers an unusually complete storage setup for an 8L vest, a proven comfortable fit, and flexible pole carrying. If you value organised storage, breathability and a dial-in fit over sheer capacity, this is an easy vest to recommend. Just factor in the potential £20 pole quiver if you race in the mountains regularly.

Conclusion

After a month of testing, the Fuger Air8 V4 continues KAS’s strong track record. It is light, comfortable, exceptionally well organised and packed with thoughtful touches like the locking bite valves, silicone-lined flask pockets and removable rubbish bag. The catching plastic toggles are a minor annoyance rather than a dealbreaker, and everything else about the vest works the way you want it to on the trail. For anyone shopping for a lightweight hydration vest, this one deserves a close look.