Nylon Designed to fit our Backcountry Bed and sleeping pad Large U-shaped opening to make getting in and out easy Mesh window panel for ventilation in good weather Waterproof/breathable top fabric for increased comfort Guy line loop to increase peak height of bivy for increased comfort Designed to fit our revolutionary Backcountry Bed and a 2.5" inflatable pad on the inside of the bivy, so you can sleep as comfortably on a rock ledge as you do at home. Sleep how you want, where you want. Top Fabric: 20D Nylon Ripstop WPB, DWR/10,400MM PeU, 18,300 g/day MVTR Bottom Fabric: 30D Nylon Ripstop, DWR/1200mm PeU, FR CPAI84