If your pack doesn’t come with a cover then you need one of these, the Sea to Summit Ultra-Sil Pack Cover is made from tough and durable 30D Ultra-Sil® siliconised Cordura® with a hydrostatic head of 2,000mm to protect your pack from heavy rain. Many packs are manufactured from highly water resistant fabrics but the many seams in their construction make it almost impossible to make them waterproof. The Ultra-Sil Pack Cover with its ‘no seam’ construction solves this problem so why don’t you do what I do and use dry bags on the inside and a rain cover on the outside to absolutely guarantee your gear stays dry.Sea to Summit Ultra-Sil Pack Cover Medium Features: 30D Ultra-Sil® Siliconised Cordura® 2,000mm Waterhead “No Seam” Construction for Water Resistance Mid-Back Keeper Strap on Sizes S - L Packaged in its Own Ultra-Sil® Stuff Sack Drainage Hole on the Base Medium fits 50 Litre to 70 Litre Packs