Forever end the debate about whether you can afford the extra weight of an Sea to Summit Ultra-Sil Pack Cover, the medium size weighs less than 4 oz and packs into a tiny stuff sack.Features: Made of 30D Diamond Ripstop silicone impregnated Cordura, so its waterproof finish can't peel or wear off over time Siliconized Cordura is about one third the weight of traditional coated nylon This pack cover uses a no seam construction for complete waterproofness Comes packaged in its own mini siliconized nylon stuff sack that remains attached to the cover so it can't get lost Comes in four sizes to fit daypacks up to large backpacks Specs: Size: Medium Length: 28" Width: 16" Height/Depth: 10" Weight: 4 oz Volume: 50 liter to 70 liter