The original Jerven Fjellduken lightweight unlined bivouac bag is large enough to sit in, ideal as a poncho, under which the backpack still finds its place. The outer material of the Duken Fjell is completely coated with aluminium and waterproof. Thanks to the aluminium coating, the heat is radiated, as with an emergency blanket. A disadvantage is the condensation that is formed. However, the outer skin is deliberately 100% waterproof and windproof. When sitting in the swamp, the breathable fabrics are not dense enough. And in addition, they allow heat to escape. Both side opening zippers, sleeve openings and reinforced eyelets provide a variety of uses. So it can be used as a poncho, tarpaulin, bivouac bag, bean bag and even as a hammock. During the tests carried out by the Oulo Regional Institute in winter, at an outdoor temperature of -10°C, the temperature inside the closed Jerven Fjellduken Thermo was +15°C – a temperature difference of 29°C. The only source of heat was the person inside the bivouac bag. The Jerven Fjellduken Original achieved a temperature difference of 9°C in the same test. What is Fjellduken? In Norway, the invention is commonly known as "Fjellduken" or "Jervenduken". In the first place, it was designed as a waterproof and windproof poncho for hunters, but can also be used as a bivouac or flexible tent tarp to use. Jerven backpack can protect both one person and backpack from rainfall and cold. It can be used as a roof construction for an entire group or as a sleeping bag or cover for the sleeping bag. Thanks to its versatility and thoughtful design, the Jerven bivy bag can be used in the same way as it is needed. The Jerven Fjellduken has been successful in the Norwegian army since 1983