Filson Rucksack in Otter Green. This Filson bag is created from rugged twill, which is Paraffin treated industrial weight 100% cotton and densely woven for strength and long lasting toughness. It is highly water repellent, ideal for the British winter. Over the years, Filson's philosophy has never changed: Make sure it's the absolute best. This rucksack is an investment piece after all comfort, protection and durability never go out of style.