I like that. Multi-use makes it even more attractive.
If you dont have spare insulation then just head to your local thrift store and buy and old coat. Cut the arms off below the elbows and stitch them together. Voila'! You have yourself an ultra cheap Hand-warming pouch. Feed some webbing through it with a buckle and hang it from your waist. Should be able to make one for the cost of an old coat and 40" of webbing and a buckle.