The space-type emergency blankets are basically metallized plastic - and they WILL melt and/or catch fire if exposed to open flames. A more robust version of this is what wildland firefighters carry as their "fire shelter" of last resort, more commonly known as a "shake 'n bake." Those can stand hours of radiant heat, but only a few minutes of direct heat.
The "sportsman's blankets," which usually have some kind of ripstop nylon cloth backing, are a better choice if you want durability and versatility.
And there have been extensive discussions both on the Survival Forum and in ETS about the fact that the space blankets do little more than act as a wind or water barrier - they are not going to get you all toasty warm on a bitterly-cold night.