Sea to summit ultra sil dry sack green 20 litre sea to summit ultra sil dry sacks are more than 50 lighter than our super popular lightweight dry sacks theyre made of siliconized cordura which is one of the lightest and toughest waterproof nylon fabrics available now you dont have to choose between keeping your gear dry and keeping it light features a backpacker magazine editors choice award winner super compact and ultra lightweight made of ultra siltm nylon a polyurethane