Used once for mountain climbing. How about this for routes that require a helmet, but you don't have much space in your backpack, or for cycling trips where you transport your bike? *Please check my profile before commenting. The following is a quote from the Montbell official online shop: This is a holder for attaching helmets and clothing to the outside of your backpack. It uses stretch material, so it can accommodate helmets and clothing of various sizes. [Compatible Backpacks] Medium to large backpacks with two side tapes (width less than 2cm) on each side. Specifications [Weight] 77g [Color] Black (BK) [Size] Height 24.5cm x Width 23.5cm