Some of the heavier mil plastic is superior in terms of ripping vs a space blanket. Niether do very well around fire. The space blanket is superior as a fire reflector. Both can be improved by hemming the edges with ductape. Plastic beats space blankets in cost and in refolding. If I was packing an ultralight kit a spaceblanket used along with natural materials for shelter is my choice. In my minimal rucksack kit I pack a 9'x9' nylon sill tarp with premade lines and stakes.