WHAT’S THAT BIT FOR?

Q I’ve noticed that quite a few rucksacks have elastic bits on the shoulder straps, what’s the deal here? Claire Spencer, via email

Trail says The majority of rucksack shoulder straps feature elastic bands that straddle the strap. These are designed to secure hydration tubes. If you have a hydration bladder in your pack, feed it through the top of the sack (there’s normally a specific outlet) and run it under the elastic band. This keeps the mouthpiece in a convenient place so you can drink on the go and also stops the tube flapping about. Note, in the picture above, the grey band below is for holding sunglasses.