to cut the smallest piece off of that 20x20 tarp. They all 'think" that they want these HUGE shelters when all that does is dissipate their body heat and require them to have fire for heat, which of course means lots of time and energy wasted on firewood. They are forbidden to cut up the 10x10 tarp, but nothing is said about the 20x20 tarp. If they'd bring the 12x12 tarp and the duct tape, they could make a SEALED supershelter, 4x4x7 ft, out of 100 sq ft of the 12x12 tarp, half reflective and half clear tarp. This includes the double layer of clear material. Another 50 sq ft of the 20x20 tarp is needed later, for the double walls for the rear and sides of the shelter, stuffing debris between the layers. Given all the clothing that they can wear, with debris between the layers and up on a raised wooden bed, such a shelter requires no fire for heat and no sleeping bag, down to at least 0F. that would easily cover them until they get the 2 inches of snow needed to make an igloo.