Look for a comfortable, close fit, that won’t bounce around. You’ll need a capacity of 10-20 litres. Soft, stretchy, mesh fabric is good, a hip belt is essential, and chest belt is useful. A hydration option is not essential. Look for shoulder straps that are padded but not bulky
Salomon Agile2 12 Set
Impressively light (380g, for 12L), the excellent stretch-fit fabic means it moves with your body, and even when full isn’t rigid or uncomfortable.
OMM Classic 25L
Designed for mountain marathons, this popular pack sits snugly to the back with good padding. It’s light and stretchy, with useful zipped belt-strap pockets and comfy straps.
Berghaus Vapour 15 Rucksack
Comfortable and light, this pack is more rigid than some, but a clever airflow system prevents sweaty backs. It includes a quick-access water bottle.
Osprey Rev 1.5
A smaller backpack, but fits an extraordinary volume of gear inside. Comfortable fit with mesh back to prevent accumulation of sweat. The pack as many extra features however the most useful is the flip down phone/GPS pocket which means you don’t have to interrupt your activity to look at your device.