The sea to summit pack liner s will give you fantastic protection and cheap insurance for the gear in your backpack or rucksack when faced with torrential rain and river crossingsdesigned to fit 50 litre rucksacks the sea to summit pack liner s is a fully waterproof seam sealed roll top bag that will protect your possessions from the wet great for situations where you may be faced with torrential rain or river crossingshardwearing this pack liner features a unique non wicking hypalon roll