Best Hydration Backpacks for Marathon Training in 2026
When I started training for ultras, I quickly outgrew hydration belts. Twenty miles in the hills with only 500ml of water is a recipe for suffering. A hydration backpack changed everything — two litres of water, space for food and layers, and hands completely free. But not all running vests are created equal. Some bounce like a rucksack on a trampoline, others rub your collarbones raw by mile 10. Here is what works after testing several across a full ultra training cycle.
When Do You Need a Hydration Backpack?
For most road marathon training, a handheld bottle or belt is sufficient. You need a backpack when your runs regularly exceed 2 hours, when you are running remote trails without water access, or when you need to carry mandatory kit for fell races and ultras. If your longest run is 16 miles on roads with shops along the route, you probably do not need one yet.
The Vests That Earned Their Place
Salomon ADV Skin 12 — Best Overall Running Vest
This is the gold standard of running hydration vests and the one I use for races. The fit is remarkable — once adjusted, it moulds to your torso and genuinely does not bounce, even on steep descents. Two 500ml soft flasks sit on the chest for easy access while running, and the 12-litre capacity handles all mandatory kit for most UK ultras. The stretch mesh pockets on the front hold gels, phone, and a waterproof jacket without needing to stop. It is expensive at around £130, but it is the vest I have seen on more ultra start lines than any other.
Nathan VaporAir 2.0 — Best for Hot Weather
Nathan built this vest with ventilation as the priority. The mesh back panel sits away from your body, allowing airflow underneath. The 2-litre bladder sits flat against your back, and there are two additional front flask pockets. It runs warmer than the Salomon in terms of capacity (7 litres), but for summer training runs and warm-weather marathons, the breathability makes a genuine difference to comfort.
Decathlon Evadict 5L Trail Running Vest — Best Budget
At around £30, this Decathlon vest is remarkable value for runners trying hydration vests for the first time. Two 500ml soft flasks are included, the fit is adjustable and reasonably secure, and there is enough storage for gels, phone, and a light layer. It does not match the Salomon for fit or bounce control on technical terrain, but for road marathon training and casual trail runs, it is more than adequate. Start here if you are unsure whether a vest is for you.
Bladder vs. Soft Flasks: Which Is Better?
Bladders (the reservoir with a drinking tube) carry more water and distribute weight evenly across your back. Soft flasks sit on your chest and are accessible without a tube. I prefer soft flasks for runs under 3 hours because I can see how much water I have left and refill them easily. For longer efforts where I need more than a litre, I use a bladder. Many vests accommodate both, so you do not have to choose permanently.
Getting the Fit Right
- Try it loaded: Fill the water and pack it with everything you would carry, then run. An empty vest tells you nothing about bounce.
- Adjust the sternum straps: Most vests have two adjustable chest straps. These should be snug enough to prevent bounce but not so tight they restrict breathing.
- Check for rubbing: Pay attention to collarbone, underarm, and nipple areas. If it rubs on a 5-mile test run, it will destroy you on a 20-miler.
- Size matters: Running vests are sized differently from regular backpacks. Measure your chest circumference and follow the brand’s guide. A baggy vest will bounce; a tight one will restrict breathing.
A well-fitting hydration vest opens up a world of running that belts and handhelds cannot reach. Get the fit right, fill it up, and go further than you thought possible.
