Which running vest do you need for trail running, and how should it fit?

A good running vest is one you barely notice on the trail. It sits close to your body like a firm hug, doesn't bounce on the downhills and keeps your drink within reach. Four things decide your choice: the capacity for your longest outing, the size based on your chest, how you drink (bottles at the front or a hydration bladder on your back) and where the pockets are. Get those four right and you forget you're wearing a vest and simply enjoy the path. ^[1]

On Belgian trails, that's no luxury. In the Ardennes and the High Fens you sometimes run for hours without a village, a café or a tap, and an autumn morning can swing from sunshine to drizzle in no time. If you have water, a jacket and a phone with you, you finish the day calmly. That keeps it fun, even when the weather or your legs let you down.

Do you need a vest, or will a waist belt or handheld bottle do?

You only need a vest when you have to carry more than fits in a hand or around your waist. If you run for less than an hour with water at home or along the way, a handheld bottle is enough, or even nothing. If you want to take a phone, a key and one bottle on a run of an hour or a bit more, a waist belt is light and simple. Say you run a loop in the Sonian Forest after work. A waist belt is plenty.

If you run longer than a few hours without aid stations, want to carry a rain jacket or your race prescribes equipment, choose a vest. A vest spreads the weight over your chest and your back. A full bottle on a waist belt tugs at your waist with every stride, and you feel that after twenty kilometres. Still not sure? Start with what you have and switch to a vest as soon as you notice you're missing something out there.

How many litres do you need?

The capacity in litres tells you how much fits in all the pockets together, a bit like the size of a suitcase. Running vests range from about 4 to 15 litres. A vest of 4 to 8 litres is made for short training runs with water nearby and for races. It's compact and stays light, but a thick jacket and a full lunch fit in tightly. ^[1]

For a long trail outing without aid stations, choose 8 to 12 litres. Say you run half a day in autumn around Botrange in the High Fens. Then you want drink, food, a jacket and a warm layer with you, and that fits in this class. Vests of 12 to 15 litres are for full-day outings, and also for when you combine running and hiking or switch sports along the way. ^[1]

For a race, let the mandatory equipment list decide, not your gut feeling. On a short trail you sometimes need very little: for the races in the 20K category, the Eiger Ultra Trail by UTMB requires only a phone, a cup, 0.5 L of water and a whistle. A waist belt or a small vest is enough for that. For the 100 km, the same rules require, among other things, at least 1 L of water, two headlamps, a survival blanket, a food reserve, a waterproof jacket with a hood, trousers that cover your whole legs, and a warm long-sleeved layer. All of that has to fit in your vest, on top of the food and drink for the race itself. For the food reserve, the organiser recommends 800 kcal. So check the list for your own race and edition, and pack your vest with it before you buy. ^[3]

How should a running vest fit?

Choose your size by your chest circumference, not by your height or your back length: manufacturers mostly work with chest circumference. Measure with a tape measure under your armpits, around the widest part of your chest, and compare that with the brand's size chart. Empty, the vest should sit close to your body everywhere, like a firm hug. There should still be room to pull the straps tighter, because your vest gets lighter as you drink and eat. ^[1]

Snug doesn't mean tight. The vest shouldn't bounce or swing, but you should still be able to breathe freely. Take a deep breath in the shop: if you feel the straps cutting into your ribs, it's too tight. Experienced runners adjust the straps as they run: a bit looser uphill, where you breathe deeply, and a bit tighter on technical terrain, where you don't want to feel jolts with every leap over roots. ^[2]

Always try a vest on filled. An empty vest sits differently from one with water and gear in it, and you only notice the bouncing once there's weight in it. Bouncing mostly comes from a vest that's too loose or too big, not from the brand or the model. Spread the weight over the front and the back, and the vest stays most stable. ^{[1] [2]}

Women and a larger chest: what do you look out for?

For women, the position of the chest straps decides whether the vest is comfortable. Salomon's fit advice: the upper chest strap at the level of the bust or just above it, the lower one in line with the bottom of your rib cage. Move the straps both in height and in width until it fits well. Small shifts already make a big difference. A vest whose straps you can't move only fits you if they happen to sit in the right place. ^[2]

Women's models usually have a shorter torso, straps in a different place for different bust sizes and pockets that sit differently. The straps sit differently to prevent chafing. At the front, soft flasks work better than hard drinking bottles: hard bottles press on the chest, soft flasks shape themselves to your body. If you have a larger chest or a long torso, try both a women's and a unisex model, filled. Choose the model where the straps stay above and below your bust, not the model whose label lists the right gender. ^{[1] [2]}

Runners with a higher body weight or a broad chest

Here too, start with the chest chart, not with your T-shirt size. Choose a vest where you still have strap to spare when you put it on. That way you can loosen it later if you wear a warm layer under the vest. Look at the edges under your armpits: soft, rounded edges chafe less than a stiff seam when your arms swing past. If you're torn between two sizes, take the one where you can still pull the straps with the vest loaded tighter, not the one where they're already at the very end.

Soft flasks or a hydration bladder?

Soft flasks are bottles of flexible plastic in the pockets at the front, which collapse like a balloon as you drink. You grab them without stopping, you see how much you have left and you can put something different in each one, for example water in one and sports drink in the other. Together they usually hold about 1 L. One downside: putting a flask back into a full vest is tricky while running. ^[1]

A hydration bladder is a plastic bag with a tube that sits in the back of your vest. It gives you 1.5 to 2 L extra, but it takes up room you would otherwise use for a jacket. Your back gets warmer, you have to take the vest off to refill it, and the water sloshes as it empties. Choose soft flasks for races with aid stations and for training runs with a tap along the way. Choose flasks at the front and a hydration bladder for a long summer outing in the Ardennes without aid stations. ^[1]

Which pocket do you use for what?

Put what you need often at the front. You can reach the pockets on your shoulder straps while running, but for the pockets on your back and at the bottom you usually have to stop and take the vest off. Gels, a bar, your phone and a tissue belong at the front. A rain jacket, which you only put on now and then, goes at the back. In the shop, also check whether you can open and close a pocket with one hand: with cold fingers on a wet winter morning, that counts. ^[1]

How warm does a running vest get?

The more fabric on your back, the warmer you get. Vests made of light fabric and mesh, a fine net with little holes like in a sports shirt, let the air through better. Smaller vests of 4 to 8 litres stay cooler, and a back full of gear ventilates worse. Going uphill in the Ourthe valley in July, you feel that difference. In winter, a warm back is actually pleasant. If you mostly run in summer, choose the smallest vest your gear fits in. ^[1]

Buying second-hand and looking after your vest

If your budget is tight, a second-hand vest is a good choice, as long as the fit is right and the parts are intact. A vest wears mostly at the zips, seams and buckles. Thicker, less stretchy fabric lasts longer. Test every zip along its whole length, pull on the elastic of the pockets and the straps (slack elastic no longer keeps your flasks in place), and check whether the seams under the armpits and at the shoulders still hold. Unscrew the flasks or the bladder, rinse them out and smell them, and check the bite valve: the little cap you drink from should close without leaking. If you doubt the flasks, replace just those and keep the vest. ^[1]

Care is simple and makes your vest more resistant to wear. After a sweaty or muddy run, rinse the vest with lukewarm water, so salt and sand don't attack the fabric and the zips. Wash it by hand instead of in the machine, and the elastic and seams stay good for longer. Let flasks and bladder dry open, and they won't smell musty on your next run. ^[1]

How to start this week

Grab a tape measure, measure your chest circumference and write down what you want to carry on your longest outing of this season. Take that list, your own flasks and the checklist above to a shop, or use them to look at a second-hand vest. Then pick a route from the RouteRadar library or upload your own GPX, and let Pre-Flight check your route before you set off. Pack the vest at home as you would for the real outing, tell someone which route you're running, and save 112 as your emergency number. Then comes the best part: a first long run where you simply forget your vest.

Field notes · Route library