Diane Bulley wrote:Sorry, that should be Space Blanket.
clue's in the name DB...ie space.
they're next to useless when you're in a sleeping bag in a tent, as heat is mostly carried away by conduction (contact with the ground, and convection, ie. you warm up the air near you and it rises to be replaced by new cold air.
the amount lost via radiation is minimal, unless you're in outerspace and have no air to lose heat to, and no ground to lay on, then it will be the case that your entire heat loss is by radiation.
whilst i acknowledge that they are given to marathon runners, it would be impossibly bulky for a marathon organiser to give everyone a proper fleece suit to keep them warm, and the wind chill (convection) is much greater on a wet body, hence why we sweat when we're hot. they do work on marathon runners as a wind proof membrane, but little more.
you don't see north pole explorers in anything else but big suits of trapped air pockets, and the same is true of your loft and hot water tank (hopefully)
if you're cold because of too little insulation (sleeping bags, socks, hats etc.) then the only answer (as R2 states) is the burning of hydrocarbons