I carry both, a space blanket, and a large black garbage bag (which if necessary can be cut to yield a decently large plastic tarp.
To carry the space blanket, I folded it into about a 10 inch square and put it into a ziplock bag. Then I pressed it flat to remove all the air. This makes for a flat package, and prevents any crinkling.
I keep both the space blanket and the heavy garbage bag (folded to a similar size), as well as a folded orange reflective vest, in the rear "game" pocket on my Scott eVest.