Performance
Space and Access
The K4 as a pack system is as scalable and adjustable as you can dream of. There are 4 different bag sizes – each bag is distinct in design as they serve slightly different purposes: 2200 daypack, 3600 extended weekender bag (or a lightweight week bag), 5000 all-year weekly bag, and 7200 one for long expeditions – anywhere, anytime. Add to this a removable lid, and the K4 system allows for any volume starting from 2200 cu-in and up to almost 8k cu-in… plus that frame-cargo space. All bags except the smallest one share a roll-top top-loader design, and all have additional side or front openings for easy loading and quick access to any part of the bag. All pockets can be quickly accessed too and all zippers are glove-friendly. The 2200 cu-in pack is a panel loader style with an integrated lid pocket – a very convenient solution on a daypack. Overall, it’s evident that the K4 system was designed for and by avid outdoors people.
Pockets and Organizing
Depending on bag size, the organizing can vary. Still, as a principle, you get one substantial central cavity, a dedicated hydration bladder compartment, two long side zipper pockets, and two side open pockets. The hydration pocket has a waterproof lining, so the pack’s interior will not get wet in case of a bladder leak. The 2200 daypack has a slightly different configuration with an additional top pocket and inside “hidden” zipper, as it’s by default a bag to be carried without the additional lid. However, with the optional strap extenders, you can use the K4 lid also on the smallest bag. Long side pockets are great for a spotting scope, tripod, or other heavy and long objects you’d like to protect from the elements. Side “bottle pockets” can be used with compression straps going crosswise inside, leaving the pocket open for storing bottles, a cooking system, or a rolled jacket. Or with compression straps over them to tighten down long objects that are partly kept inside (like a tripod). There’s even a tiny flat extra pocket there with an opening accessible with a pack on the back, which is great for snacks or for clipping a pocket knife inside. My 3600 cu-in bag also had a stretch front pocket, which I used mainly for quick-access items like my rain jacket (folded flat). And you have the lid – a removable, spacious, double compartment. It’s a classic design with no frills and no gimmicks, and it stays perfectly in place when cinched down with front and back straps.
The K4 has PALS slots on the straps and waistband. I avoid adding bulky pouches to my waist belt as they often interfere with natural arm movement, but a slim pocket on a belt is always welcome. The dedicated K4 Hipbelt Pouch holds my EDC kit ready and close at hand. I also usually carry a small fixed blade on my shoulder strap, and with the K4’s attachments it was comfy and easy.
But the real hidden treasure is the way the Exo guys attached the Nalgene bottle holder – at about a 30-degree angle, located between the waist belt and the bag. It never gets in your arms’ way and is naturally easy to access with the pack on your shoulders. Why did no one think of such a water bottle placement before? It’s brilliant!
And finally – using the cargo space. To use it, unbuckle the side compression straps, release the lid held by the top hooks, and open the cargo area between the frame and bag. Now, you can place the load, tighten it to the frame firmly with dedicated straps, and re-attach the bag. Buckle up all straps, attach the lid, and you’re ready. The whole process is considerably easier and faster than it was on the K3. The angled compression straps prevent the bag from sagging, so a pack with cargo sits balanced on the back. If the object you need to carry is wider at the bottom, you can also lose the bottom compression strap and create a cargo shelf. But in most cases, it’s still better to carry the additional load high, wedged in a V-shaped space between frame and bag.
Comfort
The frame and support are the most critical aspects of a heavy hauling pack. Not the weight, not the bag design, but the frame and carry system are everything if you put 80-100 lbs on your back. The base weight of the K4 3600 (frame, pack, lid) is just 5 lbs 8 oz, and it is remarkably lightweight for an external frame pack of this comfort. It’s even lighter than many classic internal frame packs of this size! In a base camp hauler or a cargo-carry pack, a couple of ounces more or less do not matter – but comfort and strength do, oh yeah! Big external frame packs are entirely different animals than ultralight packs, which seldom carry more than 40 lbs.
The K4’s entirely new carbon frame transfers hefty load via an upgraded carry system and distributes that weight to the hips and torso of the carrier. But that frame still has some flex, so it follows all the body movements. The shoulder straps and an enormous waist belt are well padded with special foam, which the Exo guys selected after months of testing of various types. The lumbar pad is sized to support a heavy pack, but the foam inside is not the same as in the pack’s shoulder straps. It’s also very different from what other brands use in classic packs. The standard foam would instantly compress to almost zero cushioning under a fully loaded 7200 cu-in pack plus 60+ lbs of cargo load. But that special K4’s lumbar pad works great, and together with the waist belt, they transfer most of the weight to the hips. That is more comfortable and safer for the backbone than putting excessive weight on the shoulders. Undoubtedly, it’s the most comfortable heavy hauler I’ve ever had on my back!
To ensure maximum comfort, you first need to measure your body and order a specific size of frame and belt, then micro-adjust it to your body shape. It’s easy and intuitive, but you can still check Exo Mtn Gear’s excellent video guides to ensure a perfect fit. The back panel and straps give some ventilation and keep sweat away thanks to heavy-duty mesh. But if you think you won’t sweat when carrying 80 lbs for a couple of hours in the mountains – you are wrong. No pack would help you in this regard – the brutal truth is, the only help can be your stamina and training throughout the year, well before hiking season starts.
The K4 remains very comfortable in a daypack mode but is still heavier than most dedicated daypacks. Even with the smallest 2200 bag, the system at 4lbs 9oz is not lightweight by today’s standards of alpine packs. However, the K4’s primary role (as a pack made with mountain hunters in mind) is to bring that weighty game back to the base camp at the end of the day. But it would also work great as a recon pack for the backcountry or as a platform to carry a heavy and bulky load one way to the camp (to be used later in a daypack configuration). I hiked and even scrambled quite a lot with the dedicated 2200 cu-in panel-loader bag or a compressed 3600 one (after utilizing its total capacity as a base camp pack). It worked fine, but a full-size frame is still more optimized for backcountry hiking than climbing or scrambling. So, for pure non-hunting use on technical routes, via-ferratas, or for moving in rocky vertical terrain, I’d instead use a lightweight and agile dedicated climbing pack, which I could still carry comfortably between the K4 bag and frame on approach to the base camp or mountain shelter.
Weatherability
It’s a seriously weatherproof pack, and I tried it the hard way! The main fabric is waterproof, so it’ll be fine in light rain or snow. But still, some water can leak to the inside through stitching lines, especially during a long-lasting downpour. If this is your primary concern, use either an aftermarket rain cover or (better) get a dedicated waterproof drybag insert for your pack. Exo offers them for all bag sizes except the 2200 daypack. Additionally, you can Velcro these bags inside for perfect fit and operational convenience. Only a sealed drybag like this provides total waterproofness – so if you expect super rainy weather or when crossing rivers and waterfalls, there’s no better option for you. Of course, the lid or side pockets are still unprotected, and side access to the bag is impossible – but that’s a compromise I accept. Still, it’s the best solution to protect your main gear from water. As a side note – remember that a fully sealed pack can sometimes be more of a nuisance than a benefit. Especially on more extended expeditions, it can prevent moist clothing from breathing and drying out, which can quickly start gross issues like odor or mold buildup inside a pack.
