The lightweight, unlined Jerven Fjellduken original bivouac bag is large enough to sit in, excellent as a poncho under which the backpack still has space. The outer material of the fjelldukes is completely aluminium coated on the inside and waterproof. Thanks to the aluminium coating, the heat is radiated back like a rescue blanket. One disadvantage is the condensation that forms. The outer skin is deliberately 100% waterproof and windproof. When you sit in the swamp, breathable fabrics are not tight enough. And they also allow heat to escape. The zippers, sleeve passes and reinforced eyelets offer a variety of uses. So it can be used as a poncho, tarp, bivouac bag, bean bag and even as a hammock. During tests of the Oulo Regional Institute in winter, at an outdoor temperature of -14°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". Primarily it was designed as a wind and waterproof poncho/wind protection for hunters, but can also be used as a cloth bivouac or flexible tent tarpaulin/tarp. The Jerven bivvy bag can protect both one person and the backpack from rain and cold. It can be used as a roof construction for a whole group or as a sleeping bag or cover for the sleeping bag. Thanks to its versatility and thoughtful design, the Jerven bivouac bag can be used just as it is needed. The Jerven Fjellduken has been successful in the Norwegian army since 1983