The lowe alpine airzone pro backpack can be extended from 33 litres to 40 for the extra gear you might need to carry this is ideal for when you struggle to repack your gear once youre already out and about features airzone back system tensioned mesh construction for increased breathability comfort and reduces weight to aid you on your hikes on arduous trails adativefit harness adjustable carry system allows for complete comfort expandable volume nd fit narrower dimension specifically