When you start trail running, you quickly understand one fundamental thing: running in nature requires a certain level of autonomy. The trail running backpack is not just a "backpack" to carry your things, it becomes a true second skin. Well-chosen equipment greatly enhances your comfort, pleasure, and performance. On the other hand, a poor choice quickly turns into a nightmare: painful chafing on the neck, constant bouncing with each stride, or the inability to grab your water flask without twisting yourself.
The problem? Facing store shelves or online shops often causes panic. Which brand should you prioritize? What volume should you choose? Should you opt for front flasks or a hydration bladder in the back? The selection is now overwhelming and it is very easy to get lost.
Don’t panic! This article is designed as a step-by-step guide to help you see clearly. Whether you are preparing your first 15km in the forest or aiming for the finish line of a legendary Ultra-Trail, we will break down all the criteria together to help you find the perfect trail running backpack: the one you will completely forget about during your effort.
Step 1: Define the volume (capacity) according to the distance
This is THE question you must always start with. In trail running, the size of the pack is expressed in liters (L). Note that this capacity refers to the total carrying capacity of your gear, not the amount of water you can carry!
The golden rule: The volume of your pack does not depend on your body size or height, but on the duration of your effort, the weather, and especially the mandatory equipment required by the race organizers.
Here is how to guide yourself to choose the right volume:
Less than 5 liters: minimalism for short formats
- For whom / Which distance? Short outings (1h to 3h), intense trainings, formats up to 20 km, or "skyrunning".
- What to put inside: Strictly the essentials. From 500 ml to 1L of water, 1 or 2 energy gels/bars, your keys, your phone, and possibly an ultra-compact windbreaker.
- The big advantage: Featherweight. The pack is so light and body-hugging that you feel completely free in your movements.
From 5 to 8 liters: versatility embodied (choice #1)
- For whom / Which distance? This is the most popular and most recommended volume for a first purchase. It is ideal for trails from 20 km to 50/60 km (efforts ranging from 3h to 6h or 7h).
- What to put inside: 1L to 1.5L of water, your solid nutrition, a real waterproof jacket with sealed seams, a survival blanket, a reusable cup, and a buff.
- The big advantage: It allows you to start safely on mountain marathons without bouncing too much when almost empty during a simple Sunday outing.
From 10 to 15 liters: ready for ultra-trail
- For whom / Which distance? Long formats (from 70 km to more than 100 miles / 170 km) and high mountain races requiring a strict list of mandatory equipment (such as UTMB, Diagonale des Fous, Templiers).
- What to put inside: The complete mountain survival arsenal. 1.5L to 2L of water, 2 headlamps, spare batteries, warm layers (long-sleeve t-shirt, microfleece), waterproof pants, gloves, a beanie, a first aid kit, etc.
- The big advantage: Excellent compartmentalization with multiple pockets to organize everything without the pack becoming a junk drawer.
- Note of caution: "Who has space, takes space." Don't overload yourself with unnecessary gear just because your pack allows it!
More than 15 liters: XXL Aadventure and fastpacking
- For whom / Which distance? Stage races in self-sufficiency (like the Marathon des Sables), ultra-light big hiking, or fastpacking (trail running with backpack) over several days.
- What to put inside: A lightweight sleeping bag, an ultra-compact inflatable mattress, freeze-dried food, a small stove, in addition to clothes and water.
Step 2: choose your hydration system (the great debate)
Water is the heaviest element you will carry, at about one kilogram per liter. How you distribute this weight will radically change your running comfort. Historically dominated by the famous hydration bladder on the back, the trail market has undergone a true revolution with the arrival of soft bottles on the front. Here is an objective comparison to help you decide.
| Hydration System | Major advantages on trails | Limitations to consider |
|---|---|---|
| Soft Bottles (on the front) | Perfectly balances the weight by offsetting the back gear. Allows lightning-fast refilling at aid stations and offers the possibility to alternate water and isotonic drinks. The remaining water level is always visible at a glance. | May create a slight compression feeling on the ribs at the start. An unpleasant bouncing effect is possible if the pocket fabric loosens with wear. |
| Hydration Bladder (on the back) | Provides massive carrying capacity (up to 3L), ideal for long self-supported adventures. Frees precious space in front of the pack for nutrition and allows continuous hydration through the tube. | Usually very laborious filling requiring pack removal. Generates regular sloshing noise with each stride and does not allow easy gauging of how much water remains. |
The indisputable verdict
Unless you are setting off for a long hike or a fully self-supported trail in the desert, we strongly recommend front soft bottles. This is the choice of the vast majority of runners and elite athletes today, for obvious reasons of practicality, posture balance, and time gain at aid stations.
Step 3: ergonomics, support, and morphology
Forget everything you know about traditional backpacks. A trail pack is not worn, it is put on like a garment. It must become one with you.
backpack vs. hydration Vest
If you look at current models, you will see that they resemble sleeveless vests more than traditional backpacks. This "vest" cut envelops the ribs and distributes the load across the entire torso instead of pulling only on the shoulders. It is now the absolute standard to avoid side-to-side swinging.
how to choose the right size?
This is beginners' number 1 mistake: buying a pack that is too large "to be comfortable."
- A pack too large will move with every stride. This constant bouncing will cause chafing, burn your skin around the neck or collarbones, and exhaust you mentally.
- What to do? Measure your chest circumference (like for a t-shirt) and rely on the brands' size guides. If you hesitate between two sizes, choose the smaller one. The pack must be tight and pressed against you. Lacing systems or elastic sternum straps will allow you to adjust it to your breathing. Caution: try it on if possible over a thin t-shirt, but also imagine it with one or two additional layers in winter.
Step 4: storage, accessibility, and pole holders
Comfort during the run is measured by one simple criterion: not having to take off your pack. Everything you need during the effort must be at your fingertips without having to contort yourself.
front and side pockets
This is the nerve center of your organization. These spaces are crucial for storing your nutrition (gels, bars), your phone, and empty wrappers. Favor models offering very stretchable fabric pockets to maximize volume without creating pressure points. The presence of a specific pocket closed with a zip is a huge asset for securing your keys or smartphone.
The kangaroo pocket (or tunnel) at the back
This is the major innovation of recent years on trail packs. Located on the lower back and open on both sides, it allows you to grab or stow your windbreaker while running simply by sliding your hand behind your back. It's an undeniable time and fluidity gain, especially facing changing mountain weather.
managing trail poles
Carrying folded poles without disrupting your stride or arm swing is an art. Here are the three main solutions offered by manufacturers to help you choose:
| Attachment system | Functioning and advantages | Disadvantages to consider |
|---|---|---|
| On the front (on the shoulder straps) | Vertical fixation along the soft bottles. Super quick access, perfect for courses with frequent accelerations. | May hinder arm movement or complicate access to the water bottles depending on the models. |
| At the back (horizontal or diagonal) | Elastics located at the lower or middle back. Completely frees the front of the body and the range of arm movement. | Requires some shoulder flexibility to grab and stow them while running. |
| The quiver (additional accessory) | An inclined tube fixed on the back where poles are slid. Child's play manipulation and maximum running comfort. | Adds a slight cost and a bit of extra weight. Compatibility with your pack must be checked. |
Step 5: the small details that make a big difference
Once volume, hydration, and ergonomics are validated, focus on the finishing touches. These are often what justify the price difference between an entry-level bag and a technical model.
The material requirements
Systematically look for a "3D Mesh" (a very airy honeycombed fabric) on the back and the inner side of the shoulder straps to ensure optimal sweat evacuation. Additionally, the presence of at least one pocket with a waterproof inner lining is a valuable detail to protect your electronics from rain and your own sweat.
Mandatory safety elements
The survival whistle is not a comfort option; it is a strict requirement for almost all official races. Make sure it is well integrated into the bag (usually attached to a small strap at the front). The presence of reflective prints on the front and back is also essential to be seen during your night training sessions.
The trap of extreme lightness
Be careful of the obsession with ultra-light bags! While gaining a few dozen grams is tempting on paper, it often comes at the expense of fabric durability and comfort (less padded straps, fragile nets that tear at the first branch). A 250-gram empty bag that is comfortable and robust will always be better than a 150-gram model that cuts into your shoulders once loaded.
Ultimate tips before buying (and using)
Your choice is almost made? Before confirming your cart or checking out, keep these two absolute rules in mind.
Test under load conditions
An empty bag tried in-store is always comfortable, which is extremely misleading. To get an idea of its real behavior, don’t hesitate to add weight (with full flasks, a jacket, your phone) and jump in place. You will immediately feel if any hard points appear, if the straps cut into your neck, or if the whole thing bounces around.
Breaking in before the starting line
This is the number one rule for trail runners: never debut new equipment on race day. Take the time to tame your new bag during your long training outings. This way, you can memorize the location of each item, fine-tune the strap adjustments during effort, and spot any potential chafing areas to protect with anti-irritation cream on race day.
Conclusion
Finding your trail bag requires some method and analysis, but the reward is well worth it to enjoy your outings. Remember that the perfect model absolutely does not exist: the best bag will always be the one that precisely meets your preferred distances, fits your body perfectly, and knows how to be forgotten from the very first steps.
