Why is a trail pack different from a traditional backpack?
Before diving into the selection criteria, it’s helpful to understand what sets a trail pack apart from a traditional hiking backpack. The difference isn’t just about size—it’s an entirely different design philosophy.
A trail running pack is designed to stay stable while you run. That’s its top priority. When you run, your body sways with every stride, and a pack that bounces or swings from side to side quickly becomes exhausting.
The built-in hydration system is the other major difference. On a trail, you don’t stop to drink. Soft water bladders housed in the front pockets of the shoulder straps, or a back-mounted water bladder with a drinking tube, allow you to hydrate while running without slowing down. This constant access to hydration is essential for performance and safety in trail running.
Weight also plays a much more important role than in traditional hiking. An empty trail running pack should weigh as little as possible—between 100 and 300 grams depending on the model—so as not to hinder your run. Breathable materials, form-fitting designs, and strategically placed pockets allow you to carry the essentials without unnecessary weight.
What pack size should you choose for trail running?
This is the first question to ask yourself, and the answer depends directly on the duration and type of your run. The volume of a trail running pack is measured in liters and determines everything you’ll be able to carry with you.
0 to 5 liters: the hydration vest for short trail runs
For short runs of less than two hours, or for short-distance races, the ultra-compact hydration vest is the ideal choice. These very lightweight models, weighing between 100 and 150 grams when empty, feature two flexible water bladders on the front and a few pockets for essentials: a phone, energy gel, and a lightweight windbreaker. Nothing more, nothing less.
It offers maximum freedom of movement. Some runners describe them as “feeling like nothing at all” because the pack fits so snugly against the body. For a trail run under 25 kilometers without challenging weather conditions, this is often the best choice in terms of comfort and performance. You don’t need much in the way of self-sufficiency, as aid stations are frequent; there’s no need to carry more.
5 to 12 liters: the versatile day-hike trail pack
This is the best-selling and most versatile category. These packs cover the vast majority of trail running uses: runs lasting 2 to 6 hours, day-long trail marathons, long training sessions, and variable weather conditions. They offer enough space to carry the waterproof jacket required for many races, food, plenty of water, and safety gear.
The 8- to 10-liter capacity is the sweet spot for this category. Large enough for long runs, yet compact enough not to bounce around while running. This is the volume we recommend as the top choice for trail runners who are just starting to build their gear and want a pack that will work in any situation.
12 to 20 liters: the pack for ultra-trails and extended self-sufficiency
For ultras, night trails, races with extensive mandatory gear requirements, or mountain outings requiring you to carry warm clothing and food for several hours, pack volumes between 12 and 20 liters are essential. These packs allow you to carry a 1.5- to 2-liter hydration bladder on your back, a change of clothes, a first-aid kit, nutrition for several hours, and all the mandatory safety gear required for long-distance trails.
The challenge with these larger packs is maintaining stability while running despite their size. The best models achieve this through side compression systems—straps that compress the load to limit movement of the contents—and anatomically designed, fully supportive shoulder straps.
Allow for about 1 liter of pack volume per hour of planned hiking time, plus the volume of your hydration system. For a 4-hour hike, a 5- to 8-liter pack is appropriate. For a 10-hour hike, aim for at least 12 to 15 liters.
The hydration system: water bottles or a hydration bladder?
This is the heart of the trail running pack—its most distinctive feature compared to any other backpack. How do you carry and access your water while running? Two main systems compete, and they’re often complementary.
Flexible water pouches in the shoulder straps
Front water pouches, located in the backpack’s shoulder straps, hold flexible water bottles ranging from 150 to 500 ml. There are two advantages: access is immediate and intuitive—you simply reach forward to grab your bladder without slowing down or taking off your pack. And you can see at a glance how much water you have left, which helps you manage your hydration over the course of the run.
Most modern trail running packs include two soft flasks—one per shoulder strap—for a total of 500 ml to 1 liter of immediately accessible water. This is sufficient for short runs and for the sections between aid stations on long races.
The Backpack Hydration Bladder
The water bladder, or hydration reservoir, is a flexible compartment that fits into a dedicated back pocket and connects to a drinking tube that runs over your shoulder to your mouth. It allows you to carry an additional 1 to 2 liters of water without taking up space in your main pockets.
Its main advantage is its capacity: on an ultra-trail or a long run without frequent aid stations, carrying 1.5 liters in the hydration pack in addition to 500 ml in front-mounted flasks gives you a total water supply of 2 liters, enough for several hours under normal conditions.
The downside is that refilling it is more cumbersome. Refilling a water bladder at a resupply station requires taking off the pack, opening the compartment, filling it, and closing it—a process that takes thirty seconds but can be frustrating in the heat of the moment during a race.
A Closer Look at Women's Trail Running Backpacks
Women’s trail running backpacks aren’t simply scaled-down versions of men’s models. Women have unique body types that call for specialized designs, and the top brands have fully embraced this.
The shoulder straps on a women’s trail running pack are designed to wrap around the chest rather than compress it. The spacing between the bottom of the shoulder straps is narrower than on a men’s model, and the overall shape of the pack is adapted to a smaller back frame. The length of the shoulder straps is adjusted for shorter torsos, and the chest straps are positioned higher on the torso.
If you’re a woman and experience persistent discomfort with a unisex pack, don’t hesitate to try models specifically designed for women from brands like Salomon, Osprey, or Raidlight—brands that have invested heavily in the design of their women’s lines. The difference in comfort can be quite significant, especially on long hikes.
