I've never tried a survival bivi but I rember some articles and photos were posted. A couple of blokes hiking from Penrith following the old Roman road route towards High Street I think? I tried a tarp and bivi in May, never got on with it at all. If I tried now I could do better with the tarp but I'm still not happy with the Hunka bivy, a good bag yes, but to be useful to me it needs a zip along its length.