Sea To Summit Ultra-Sil 3L Dry Bag An ideal dry sack for backpackers who need to protect their belongings from wet weather, the Ultra-Sil Dry Sack is essential for any fast and light adventure. The Ultra-Sil Dry Bag uses a waterproof, roll-top Hypalon closure, secure with the Field Repair Buckle for a reliable seal. The dry bag will keep your essentials safe and protected from poor weather and use an ultralight and super-strong, 30D diamond ripstop siliconised CORDURA nylon, with a 2000mm hydrostatic head, so you can rely on the materials to keep your stuff dry from light rain. The pack has an oval base which helps to prevent rolling and can be packed efficiently, whilst a slippery finish slides into tight spaces in your pack or bag.