i don't have or need one..i always assumed they were a bit of mountaineering gear ment for quick shelter. no mountains around me but i get the impression it can go from ok to really bad and back again in a very short time with little space to pitch a shelter so you wear something you can hunker down in untill it clears up. the Hilleberg bivanorak is the perfect example of the quick mountain shelter.not something you would want to spent a nite in but great for a few guys to take cover in where there are few wind breaks.