A Coroplast panel gives you maybe R1-R2 tops in insulating value. Not much. But in a cold climate, it gets you out of the wind and into a dry-ish space, which is huge. And if you're somewhat functional you can quickly pile up some snow on the sides. That adds a surprising amount of R-value (which is somewhat surprising in itself; but snow holds a ton of air in tiny pockets, which is a kind of insulation, though not the snuggle-up-cozy-blanket kind).
The point of this is that the simplest of shelters can make the difference. Witness, for example, the 17-year old who survived two nights in a self-made snow shelter while rescue operations were suspended due to the weather.
http://www.washingtonpost.com/national/m...676f_story.htmlEdit: I see the snow shelter story is the subject of another thread. Probably best to make related comments over there.